<?php

/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2019 - 2022, CodeIgniter Foundation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package CodeIgniter
 * @author  EllisLab Dev Team
 * @copyright   Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)
 * @copyright   Copyright (c) 2014 - 2019, British Columbia Institute of Technology (https://bcit.ca/)
 * @copyright   Copyright (c) 2019 - 2022, CodeIgniter Foundation (https://codeigniter.com/)
 * @license https://opensource.org/licenses/MIT MIT License
 * @link    https://codeigniter.com
 * @since   Version 1.0.0
 * @filesource
 */

defined('BASEPATH') or exit('No direct script access allowed');

/**
 * Query Builder Class
 *
 * This is the platform-independent base Query Builder implementation class.
 *
 * @package     CodeIgniter
 * @subpackage  Drivers
 * @category    Database
 * @author      EllisLab Dev Team
 * @link        https://codeigniter.com/userguide3/database/
 */

abstract class CI_DB_query_builder extends CI_DB_driver
{
    /**
     * Return DELETE SQL flag
     *
     * @var bool
     */
    protected $return_delete_sql        = false;

    /**
     * Reset DELETE data flag
     *
     * @var bool
     */
    protected $reset_delete_data        = false;

    /**
     * QB SELECT data
     *
     * @var array
     */
    protected $qb_select            = array();

    /**
     * QB DISTINCT flag
     *
     * @var bool
     */
    protected $qb_distinct          = false;

    /**
     * QB FROM data
     *
     * @var array
     */
    protected $qb_from          = array();

    /**
     * QB JOIN data
     *
     * @var array
     */
    protected $qb_join          = array();

    /**
     * QB WHERE data
     *
     * @var array
     */
    protected $qb_where         = array();

    /**
     * QB GROUP BY data
     *
     * @var array
     */
    protected $qb_groupby           = array();

    /**
     * QB HAVING data
     *
     * @var array
     */
    protected $qb_having            = array();

    /**
     * QB keys
     *
     * @var array
     */
    protected $qb_keys          = array();

    /**
     * QB LIMIT data
     *
     * @var int
     */
    protected $qb_limit         = false;

    /**
     * QB OFFSET data
     *
     * @var int
     */
    protected $qb_offset            = false;

    /**
     * QB ORDER BY data
     *
     * @var array
     */
    protected $qb_orderby           = array();

    /**
     * QB data sets
     *
     * @var array
     */
    protected $qb_set           = array();

    /**
     * QB data set for update_batch()
     *
     * @var array
     */
    protected $qb_set_ub            = array();

    /**
     * QB aliased tables list
     *
     * @var array
     */
    protected $qb_aliased_tables        = array();

    /**
     * QB WHERE group started flag
     *
     * @var bool
     */
    protected $qb_where_group_started   = false;

    /**
     * QB WHERE group count
     *
     * @var int
     */
    protected $qb_where_group_count     = 0;

    // Query Builder Caching variables

    /**
     * QB Caching flag
     *
     * @var bool
     */
    protected $qb_caching               = false;

    /**
     * QB Cache exists list
     *
     * @var array
     */
    protected $qb_cache_exists          = array();

    /**
     * QB Cache SELECT data
     *
     * @var array
     */
    protected $qb_cache_select          = array();

    /**
     * QB Cache FROM data
     *
     * @var array
     */
    protected $qb_cache_from            = array();

    /**
     * QB Cache JOIN data
     *
     * @var array
     */
    protected $qb_cache_join            = array();

    /**
     * QB Cache aliased tables list
     *
     * @var array
     */
    protected $qb_cache_aliased_tables          = array();

    /**
     * QB Cache WHERE data
     *
     * @var array
     */
    protected $qb_cache_where           = array();

    /**
     * QB Cache GROUP BY data
     *
     * @var array
     */
    protected $qb_cache_groupby         = array();

    /**
     * QB Cache HAVING data
     *
     * @var array
     */
    protected $qb_cache_having          = array();

    /**
     * QB Cache ORDER BY data
     *
     * @var array
     */
    protected $qb_cache_orderby         = array();

    /**
     * QB Cache data sets
     *
     * @var array
     */
    protected $qb_cache_set             = array();

    /**
     * QB No Escape data
     *
     * @var array
     */
    protected $qb_no_escape             = array();

    /**
     * QB Cache No Escape data
     *
     * @var array
     */
    protected $qb_cache_no_escape           = array();

    // --------------------------------------------------------------------

    /**
     * Select
     *
     * Generates the SELECT portion of the query
     *
     * @param   string
     * @param   mixed
     * @return  CI_DB_query_builder
     */
    public function select($select = '*', $escape = null)
    {
        if (is_string($select)) {
            $select = explode(',', $select);
        }

        // If the escape value was not set, we will base it on the global setting
        is_bool($escape) or $escape = $this->_protect_identifiers;

        foreach ($select as $val) {
            $val = trim($val);

            if ($val !== '') {
                $this->qb_select[] = $val;
                $this->qb_no_escape[] = $escape;

                if ($this->qb_caching === true) {
                    $this->qb_cache_select[] = $val;
                    $this->qb_cache_exists[] = 'select';
                    $this->qb_cache_no_escape[] = $escape;
                }
            }
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Select Max
     *
     * Generates a SELECT MAX(field) portion of a query
     *
     * @param   string  the field
     * @param   string  an alias
     * @return  CI_DB_query_builder
     */
    public function select_max($select = '', $alias = '')
    {
        return $this->_max_min_avg_sum($select, $alias, 'MAX');
    }

    // --------------------------------------------------------------------

    /**
     * Select Min
     *
     * Generates a SELECT MIN(field) portion of a query
     *
     * @param   string  the field
     * @param   string  an alias
     * @return  CI_DB_query_builder
     */
    public function select_min($select = '', $alias = '')
    {
        return $this->_max_min_avg_sum($select, $alias, 'MIN');
    }

    // --------------------------------------------------------------------

    /**
     * Select Average
     *
     * Generates a SELECT AVG(field) portion of a query
     *
     * @param   string  the field
     * @param   string  an alias
     * @return  CI_DB_query_builder
     */
    public function select_avg($select = '', $alias = '')
    {
        return $this->_max_min_avg_sum($select, $alias, 'AVG');
    }

    // --------------------------------------------------------------------

    /**
     * Select Sum
     *
     * Generates a SELECT SUM(field) portion of a query
     *
     * @param   string  the field
     * @param   string  an alias
     * @return  CI_DB_query_builder
     */
    public function select_sum($select = '', $alias = '')
    {
        return $this->_max_min_avg_sum($select, $alias, 'SUM');
    }

    // --------------------------------------------------------------------

    /**
     * SELECT [MAX|MIN|AVG|SUM]()
     *
     * @used-by select_max()
     * @used-by select_min()
     * @used-by select_avg()
     * @used-by select_sum()
     *
     * @param   string  $select Field name
     * @param   string  $alias
     * @param   string  $type
     * @return  CI_DB_query_builder
     */
    protected function _max_min_avg_sum($select = '', $alias = '', $type = 'MAX')
    {
        if (! is_string($select) or $select === '') {
            $this->display_error('db_invalid_query');
        }

        $type = strtoupper($type);

        if (! in_array($type, array('MAX', 'MIN', 'AVG', 'SUM'))) {
            show_error('Invalid function type: ' . $type);
        }

        if ($alias === '') {
            $alias = $this->_create_alias_from_table(trim($select));
        }

        $sql = $type . '(' . $this->protect_identifiers(trim($select)) . ') AS ' . $this->escape_identifiers(trim($alias));

        $this->qb_select[] = $sql;
        $this->qb_no_escape[] = null;

        if ($this->qb_caching === true) {
            $this->qb_cache_select[] = $sql;
            $this->qb_cache_exists[] = 'select';
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Determines the alias name based on the table
     *
     * @param   string  $item
     * @return  string
     */
    protected function _create_alias_from_table($item)
    {
        if (strpos($item, '.') !== false) {
            $item = explode('.', $item);
            return end($item);
        }

        return $item;
    }

    // --------------------------------------------------------------------

    /**
     * DISTINCT
     *
     * Sets a flag which tells the query string compiler to add DISTINCT
     *
     * @param   bool    $val
     * @return  CI_DB_query_builder
     */
    public function distinct($val = true)
    {
        $this->qb_distinct = is_bool($val) ? $val : true;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * From
     *
     * Generates the FROM portion of the query
     *
     * @param   mixed   $from   can be a string or array
     * @return  CI_DB_query_builder
     */
    public function from($from)
    {
        foreach ((array) $from as $val) {
            if (strpos($val, ',') !== false) {
                foreach (explode(',', $val) as $v) {
                    $v = trim($v);
                    $this->_track_aliases($v);

                    $this->qb_from[] = $v = $this->protect_identifiers($v, true, null, false);

                    if ($this->qb_caching === true) {
                        $this->qb_cache_from[] = $v;
                        $this->qb_cache_exists[] = 'from';
                    }
                }
            } else {
                $val = trim($val);

                // Extract any aliases that might exist. We use this information
                // in the protect_identifiers to know whether to add a table prefix
                $this->_track_aliases($val);

                $this->qb_from[] = $val = $this->protect_identifiers($val, true, null, false);

                if ($this->qb_caching === true) {
                    $this->qb_cache_from[] = $val;
                    $this->qb_cache_exists[] = 'from';
                }
            }
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * JOIN
     *
     * Generates the JOIN portion of the query
     *
     * @param   string
     * @param   string  the join condition
     * @param   string  the type of join
     * @param   string  whether not to try to escape identifiers
     * @return  CI_DB_query_builder
     */
    public function join($table, $cond, $type = '', $escape = null)
    {
        if ($type !== '') {
            $type = strtoupper(trim($type));

            if (! in_array($type, array('LEFT', 'RIGHT', 'OUTER', 'INNER', 'LEFT OUTER', 'RIGHT OUTER', 'FULL OUTER', 'FULL'), true)) {
                $type = '';
            } else {
                $type .= ' ';
            }
        }

        // Extract any aliases that might exist. We use this information
        // in the protect_identifiers to know whether to add a table prefix
        $this->_track_aliases($table);

        is_bool($escape) or $escape = $this->_protect_identifiers;

        if (! $this->_has_operator($cond)) {
            $cond = ' USING (' . ($escape ? $this->escape_identifiers($cond) : $cond) . ')';
        } elseif ($escape === false) {
            $cond = ' ON ' . $cond;
        } else {
            // Split multiple conditions
            if (preg_match_all('/\sAND\s|\sOR\s/i', $cond, $joints, PREG_OFFSET_CAPTURE)) {
                $conditions = array();
                $joints = $joints[0];
                array_unshift($joints, array('', 0));

                for ($i = count($joints) - 1, $pos = strlen($cond); $i >= 0; $i--) {
                    $joints[$i][1] += strlen($joints[$i][0]); // offset
                    $conditions[$i] = substr($cond, $joints[$i][1], $pos - $joints[$i][1]);
                    $pos = $joints[$i][1] - strlen($joints[$i][0]);
                    $joints[$i] = $joints[$i][0];
                }
            } else {
                $conditions = array($cond);
                $joints = array('');
            }

            $cond = ' ON ';
            for ($i = 0, $c = count($conditions); $i < $c; $i++) {
                $operator = $this->_get_operator($conditions[$i]);
                $cond .= $joints[$i];
                $cond .= preg_match("/(\(*)?([\[\]\w\.'-]+)" . preg_quote($operator) . "(.*)/i", $conditions[$i], $match)
                    ? $match[1] . $this->protect_identifiers($match[2]) . $operator . $this->protect_identifiers($match[3])
                    : $conditions[$i];
            }
        }

        // Do we want to escape the table name?
        if ($escape === true) {
            $table = $this->protect_identifiers($table, true, null, false);
        }

        // Assemble the JOIN statement
        $this->qb_join[] = $join = $type . 'JOIN ' . $table . $cond;

        if ($this->qb_caching === true) {
            $this->qb_cache_join[] = $join;
            $this->qb_cache_exists[] = 'join';
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * WHERE
     *
     * Generates the WHERE portion of the query.
     * Separates multiple calls with 'AND'.
     *
     * @param   mixed
     * @param   mixed
     * @param   bool
     * @return  CI_DB_query_builder
     */
    public function where($key, $value = null, $escape = null)
    {
        return $this->_wh('qb_where', $key, $value, 'AND ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * OR WHERE
     *
     * Generates the WHERE portion of the query.
     * Separates multiple calls with 'OR'.
     *
     * @param   mixed
     * @param   mixed
     * @param   bool
     * @return  CI_DB_query_builder
     */
    public function or_where($key, $value = null, $escape = null)
    {
        return $this->_wh('qb_where', $key, $value, 'OR ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * WHERE, HAVING
     *
     * @used-by where()
     * @used-by or_where()
     * @used-by having()
     * @used-by or_having()
     *
     * @param   string  $qb_key 'qb_where' or 'qb_having'
     * @param   mixed   $key
     * @param   mixed   $value
     * @param   string  $type
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    protected function _wh($qb_key, $key, $value = null, $type = 'AND ', $escape = null)
    {
        $qb_cache_key = ($qb_key === 'qb_having') ? 'qb_cache_having' : 'qb_cache_where';

        if (! is_array($key)) {
            $key = array($key => $value);
        }

        // If the escape value was not set will base it on the global setting
        is_bool($escape) or $escape = $this->_protect_identifiers;

        foreach ($key as $k => $v) {
            $prefix = (count($this->$qb_key) === 0 && count($this->$qb_cache_key) === 0)
                ? $this->_group_get_type('')
                : $this->_group_get_type($type);

            if ($v !== null) {
                if ($escape === true) {
                    $v = $this->escape($v);
                }

                if (! $this->_has_operator($k)) {
                    $k .= ' = ';
                }
            } elseif (! $this->_has_operator($k)) {
                // value appears not to have been set, assign the test to IS NULL
                $k .= ' IS NULL';
            } elseif (preg_match('/\s*(!?=|<>|\sIS(?:\s+NOT)?\s)\s*$/i', $k, $match, PREG_OFFSET_CAPTURE)) {
                $k = substr($k, 0, $match[0][1]) . ($match[1][0] === '=' ? ' IS NULL' : ' IS NOT NULL');
            }

            ${$qb_key} = array('condition' => $prefix . $k, 'value' => $v, 'escape' => $escape);
            $this->{$qb_key}[] = ${$qb_key};
            if ($this->qb_caching === true) {
                $this->{$qb_cache_key}[] = ${$qb_key};
                $this->qb_cache_exists[] = substr($qb_key, 3);
            }
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * WHERE IN
     *
     * Generates a WHERE field IN('item', 'item') SQL query,
     * joined with 'AND' if appropriate.
     *
     * @param   string  $key    The field to search
     * @param   array   $values The values searched on
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function where_in($key = null, $values = null, $escape = null)
    {
        return $this->_where_in($key, $values, false, 'AND ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * OR WHERE IN
     *
     * Generates a WHERE field IN('item', 'item') SQL query,
     * joined with 'OR' if appropriate.
     *
     * @param   string  $key    The field to search
     * @param   array   $values The values searched on
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function or_where_in($key = null, $values = null, $escape = null)
    {
        return $this->_where_in($key, $values, false, 'OR ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * WHERE NOT IN
     *
     * Generates a WHERE field NOT IN('item', 'item') SQL query,
     * joined with 'AND' if appropriate.
     *
     * @param   string  $key    The field to search
     * @param   array   $values The values searched on
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function where_not_in($key = null, $values = null, $escape = null)
    {
        return $this->_where_in($key, $values, true, 'AND ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * OR WHERE NOT IN
     *
     * Generates a WHERE field NOT IN('item', 'item') SQL query,
     * joined with 'OR' if appropriate.
     *
     * @param   string  $key    The field to search
     * @param   array   $values The values searched on
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function or_where_not_in($key = null, $values = null, $escape = null)
    {
        return $this->_where_in($key, $values, true, 'OR ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * Internal WHERE IN
     *
     * @used-by where_in()
     * @used-by or_where_in()
     * @used-by where_not_in()
     * @used-by or_where_not_in()
     *
     * @param   string  $key    The field to search
     * @param   array   $values The values searched on
     * @param   bool    $not    If the statement would be IN or NOT IN
     * @param   string  $type
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    protected function _where_in($key = null, $values = null, $not = false, $type = 'AND ', $escape = null)
    {
        if ($key === null or $values === null) {
            return $this;
        }

        if (! is_array($values)) {
            $values = array($values);
        }

        is_bool($escape) or $escape = $this->_protect_identifiers;

        $not = ($not) ? ' NOT' : '';

        if ($escape === true) {
            $where_in = array();
            foreach ($values as $value) {
                $where_in[] = $this->escape($value);
            }
        } else {
            $where_in = array_values($values);
        }

        $prefix = (count($this->qb_where) === 0 && count($this->qb_cache_where) === 0)
            ? $this->_group_get_type('')
            : $this->_group_get_type($type);

        $where_in = array(
            'condition' => $prefix . $key . $not . ' IN(' . implode(', ', $where_in) . ')',
            'value' => null,
            'escape' => $escape
        );

        $this->qb_where[] = $where_in;
        if ($this->qb_caching === true) {
            $this->qb_cache_where[] = $where_in;
            $this->qb_cache_exists[] = 'where';
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * LIKE
     *
     * Generates a %LIKE% portion of the query.
     * Separates multiple calls with 'AND'.
     *
     * @param   mixed   $field
     * @param   string  $match
     * @param   string  $side
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function like($field, $match = '', $side = 'both', $escape = null)
    {
        return $this->_like($field, $match, 'AND ', $side, '', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * NOT LIKE
     *
     * Generates a NOT LIKE portion of the query.
     * Separates multiple calls with 'AND'.
     *
     * @param   mixed   $field
     * @param   string  $match
     * @param   string  $side
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function not_like($field, $match = '', $side = 'both', $escape = null)
    {
        return $this->_like($field, $match, 'AND ', $side, 'NOT', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * OR LIKE
     *
     * Generates a %LIKE% portion of the query.
     * Separates multiple calls with 'OR'.
     *
     * @param   mixed   $field
     * @param   string  $match
     * @param   string  $side
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function or_like($field, $match = '', $side = 'both', $escape = null)
    {
        return $this->_like($field, $match, 'OR ', $side, '', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * OR NOT LIKE
     *
     * Generates a NOT LIKE portion of the query.
     * Separates multiple calls with 'OR'.
     *
     * @param   mixed   $field
     * @param   string  $match
     * @param   string  $side
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function or_not_like($field, $match = '', $side = 'both', $escape = null)
    {
        return $this->_like($field, $match, 'OR ', $side, 'NOT', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * Internal LIKE
     *
     * @used-by like()
     * @used-by or_like()
     * @used-by not_like()
     * @used-by or_not_like()
     *
     * @param   mixed   $field
     * @param   string  $match
     * @param   string  $type
     * @param   string  $side
     * @param   string  $not
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    protected function _like($field, $match = '', $type = 'AND ', $side = 'both', $not = '', $escape = null)
    {
        if (! is_array($field)) {
            $field = array($field => $match);
        }

        is_bool($escape) or $escape = $this->_protect_identifiers;
        // lowercase $side in case somebody writes e.g. 'BEFORE' instead of 'before' (doh)
        $side = strtolower($side);

        foreach ($field as $k => $v) {
            $prefix = (count($this->qb_where) === 0 && count($this->qb_cache_where) === 0)
                ? $this->_group_get_type('') : $this->_group_get_type($type);

            if ($escape === true) {
                $v = $this->escape_like_str($v);
            }

            switch ($side) {
                case 'none':
                    $v = "'{$v}'";
                    break;
                case 'before':
                    $v = "'%{$v}'";
                    break;
                case 'after':
                    $v = "'{$v}%'";
                    break;
                case 'both':
                default:
                    $v = "'%{$v}%'";
                    break;
            }

            // some platforms require an escape sequence definition for LIKE wildcards
            if ($escape === true && $this->_like_escape_str !== '') {
                $v .= sprintf($this->_like_escape_str, $this->_like_escape_chr);
            }

            $qb_where = array('condition' => "{$prefix} {$k} {$not} LIKE {$v}", 'value' => null, 'escape' => $escape);
            $this->qb_where[] = $qb_where;
            if ($this->qb_caching === true) {
                $this->qb_cache_where[] = $qb_where;
                $this->qb_cache_exists[] = 'where';
            }
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Starts a query group.
     *
     * @param   string  $not    (Internal use only)
     * @param   string  $type   (Internal use only)
     * @return  CI_DB_query_builder
     */
    public function group_start($not = '', $type = 'AND ')
    {
        $type = $this->_group_get_type($type);

        $this->qb_where_group_started = true;
        $prefix = (count($this->qb_where) === 0 && count($this->qb_cache_where) === 0) ? '' : $type;
        $where = array(
            'condition' => $prefix . $not . str_repeat(' ', ++$this->qb_where_group_count) . ' (',
            'value' => null,
            'escape' => false
        );

        $this->qb_where[] = $where;
        if ($this->qb_caching) {
            $this->qb_cache_where[] = $where;
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Starts a query group, but ORs the group
     *
     * @return  CI_DB_query_builder
     */
    public function or_group_start()
    {
        return $this->group_start('', 'OR ');
    }

    // --------------------------------------------------------------------

    /**
     * Starts a query group, but NOTs the group
     *
     * @return  CI_DB_query_builder
     */
    public function not_group_start()
    {
        return $this->group_start('NOT ', 'AND ');
    }

    // --------------------------------------------------------------------

    /**
     * Starts a query group, but OR NOTs the group
     *
     * @return  CI_DB_query_builder
     */
    public function or_not_group_start()
    {
        return $this->group_start('NOT ', 'OR ');
    }

    // --------------------------------------------------------------------

    /**
     * Ends a query group
     *
     * @return  CI_DB_query_builder
     */
    public function group_end()
    {
        $this->qb_where_group_started = false;
        $where = array(
            'condition' => str_repeat(' ', $this->qb_where_group_count--) . ')',
            'value' => null,
            'escape' => false
        );

        $this->qb_where[] = $where;
        if ($this->qb_caching) {
            $this->qb_cache_where[] = $where;
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Group_get_type
     *
     * @used-by group_start()
     * @used-by _like()
     * @used-by _wh()
     * @used-by _where_in()
     *
     * @param   string  $type
     * @return  string
     */
    protected function _group_get_type($type)
    {
        if ($this->qb_where_group_started) {
            $type = '';
            $this->qb_where_group_started = false;
        }

        return $type;
    }

    // --------------------------------------------------------------------

    /**
     * GROUP BY
     *
     * @param   mixed   $by
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function group_by($by, $escape = null)
    {
        is_bool($escape) or $escape = $this->_protect_identifiers;

        if (is_string($by)) {
            $by = ($escape === true)
                ? explode(',', $by)
                : array($by);
        }

        foreach ($by as $val) {
            $val = trim($val);

            if ($val !== '') {
                $val = array('field' => $val, 'escape' => $escape);

                $this->qb_groupby[] = $val;
                if ($this->qb_caching === true) {
                    $this->qb_cache_groupby[] = $val;
                    $this->qb_cache_exists[] = 'groupby';
                }
            }
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * HAVING
     *
     * Separates multiple calls with 'AND'.
     *
     * @param   string  $key
     * @param   string  $value
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function having($key, $value = null, $escape = null)
    {
        return $this->_wh('qb_having', $key, $value, 'AND ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * OR HAVING
     *
     * Separates multiple calls with 'OR'.
     *
     * @param   string  $key
     * @param   string  $value
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function or_having($key, $value = null, $escape = null)
    {
        return $this->_wh('qb_having', $key, $value, 'OR ', $escape);
    }

    // --------------------------------------------------------------------

    /**
     * ORDER BY
     *
     * @param   string  $orderby
     * @param   string  $direction  ASC, DESC or RANDOM
     * @param   bool    $escape
     * @return  CI_DB_query_builder
     */
    public function order_by($orderby, $direction = '', $escape = null)
    {
        $direction = strtoupper(trim($direction));

        if ($direction === 'RANDOM') {
            $direction = '';

            // Do we have a seed value?
            $orderby = ctype_digit((string) $orderby)
                ? sprintf($this->_random_keyword[1], $orderby)
                : $this->_random_keyword[0];
        } elseif (empty($orderby)) {
            return $this;
        } elseif ($direction !== '') {
            $direction = in_array($direction, array('ASC', 'DESC'), true) ? ' ' . $direction : '';
        }

        is_bool($escape) or $escape = $this->_protect_identifiers;

        if ($escape === false) {
            $qb_orderby[] = array('field' => $orderby, 'direction' => $direction, 'escape' => false);
        } else {
            $qb_orderby = array();
            foreach (explode(',', $orderby) as $field) {
                $qb_orderby[] = ($direction === '' && preg_match('/\s+(ASC|DESC)$/i', rtrim($field), $match, PREG_OFFSET_CAPTURE))
                    ? array('field' => ltrim(substr($field, 0, $match[0][1])), 'direction' => ' ' . $match[1][0], 'escape' => true)
                    : array('field' => trim($field), 'direction' => $direction, 'escape' => true);
            }
        }

        $this->qb_orderby = array_merge($this->qb_orderby, $qb_orderby);
        if ($this->qb_caching === true) {
            $this->qb_cache_orderby = array_merge($this->qb_cache_orderby, $qb_orderby);
            $this->qb_cache_exists[] = 'orderby';
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * LIMIT
     *
     * @param   int $value  LIMIT value
     * @param   int $offset OFFSET value
     * @return  CI_DB_query_builder
     */
    public function limit($value, $offset = 0)
    {
        is_null($value) or $this->qb_limit = (int) $value;
        empty($offset) or $this->qb_offset = (int) $offset;

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Sets the OFFSET value
     *
     * @param   int $offset OFFSET value
     * @return  CI_DB_query_builder
     */
    public function offset($offset)
    {
        empty($offset) or $this->qb_offset = (int) $offset;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * LIMIT string
     *
     * Generates a platform-specific LIMIT clause.
     *
     * @param   string  $sql    SQL Query
     * @return  string
     */
    protected function _limit($sql)
    {
        return $sql . ' LIMIT ' . ($this->qb_offset ? $this->qb_offset . ', ' : '') . (int) $this->qb_limit;
    }

    // --------------------------------------------------------------------

    /**
     * The "set" function.
     *
     * Allows key/value pairs to be set for inserting or updating
     *
     * @param   mixed
     * @param   string
     * @param   bool
     * @return  CI_DB_query_builder
     */
    public function set($key, $value = '', $escape = null)
    {
        $key = $this->_object_to_array($key);

        if (! is_array($key)) {
            $key = array($key => $value);
        }

        is_bool($escape) or $escape = $this->_protect_identifiers;

        foreach ($key as $k => $v) {
            $this->qb_set[$this->protect_identifiers($k, false, $escape)] = ($escape)
                ? $this->escape($v) : $v;
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Get SELECT query string
     *
     * Compiles a SELECT query string and returns the sql.
     *
     * @param   string  the table name to select from (optional)
     * @param   bool    TRUE: resets QB values; FALSE: leave QB values alone
     * @return  string
     */
    public function get_compiled_select($table = '', $reset = true)
    {
        if ($table !== '') {
            $this->_track_aliases($table);
            $this->from($table);
        }

        $select = $this->_compile_select();

        if ($reset === true) {
            $this->_reset_select();
        }

        return $select;
    }

    // --------------------------------------------------------------------

    /**
     * Get
     *
     * Compiles the select statement based on the other functions called
     * and runs the query
     *
     * @param   string  the table
     * @param   string  the limit clause
     * @param   string  the offset clause
     * @return  CI_DB_result
     */
    public function get($table = '', $limit = null, $offset = null)
    {
        if ($table !== '') {
            $this->_track_aliases($table);
            $this->from($table);
        }

        if (! empty($limit)) {
            $this->limit($limit, $offset);
        }

        $result = $this->query($this->_compile_select());
        $this->_reset_select();
        return $result;
    }

    // --------------------------------------------------------------------

    /**
     * "Count All Results" query
     *
     * Generates a platform-specific query string that counts all records
     * returned by an Query Builder query.
     *
     * @param   string
     * @param   bool    the reset clause
     * @return  int
     */
    public function count_all_results($table = '', $reset = true)
    {
        if ($table !== '') {
            $this->_track_aliases($table);
            $this->from($table);
        }

        // ORDER BY usage is often problematic here (most notably
        // on Microsoft SQL Server) and ultimately unnecessary
        // for selecting COUNT(*) ...
        $qb_orderby       = $this->qb_orderby;
        $qb_cache_orderby = $this->qb_cache_orderby;
        $this->qb_orderby = $this->qb_cache_orderby = array();

        $result = ($this->qb_distinct === true or ! empty($this->qb_groupby) or ! empty($this->qb_cache_groupby) or ! empty($this->qb_having) or $this->qb_limit or $this->qb_offset)
            ? $this->query($this->_count_string . $this->protect_identifiers('numrows') . "\nFROM (\n" . $this->_compile_select() . "\n) CI_count_all_results")
            : $this->query($this->_compile_select($this->_count_string . $this->protect_identifiers('numrows')));

        if ($reset === true) {
            $this->_reset_select();
        } else {
            $this->qb_orderby       = $qb_orderby;
            $this->qb_cache_orderby = $qb_cache_orderby;
        }

        if ($result->num_rows() === 0) {
            return 0;
        }

        $row = $result->row();
        return (int) $row->numrows;
    }

    // --------------------------------------------------------------------

    /**
     * get_where()
     *
     * Allows the where clause, limit and offset to be added directly
     *
     * @param   string  $table
     * @param   string  $where
     * @param   int $limit
     * @param   int $offset
     * @return  CI_DB_result
     */
    public function get_where($table = '', $where = null, $limit = null, $offset = null)
    {
        if ($table !== '') {
            $this->from($table);
        }

        if ($where !== null) {
            $this->where($where);
        }

        if (! empty($limit)) {
            $this->limit($limit, $offset);
        }

        $result = $this->query($this->_compile_select());
        $this->_reset_select();
        return $result;
    }

    // --------------------------------------------------------------------

    /**
     * Insert_Batch
     *
     * Compiles batch insert strings and runs the queries
     *
     * @param   string  $table  Table to insert into
     * @param   array   $set    An associative array of insert values
     * @param   bool    $escape Whether to escape values and identifiers
     * @return  int Number of rows inserted or FALSE on failure
     */
    public function insert_batch($table, $set = null, $escape = null, $batch_size = 100)
    {
        if ($set === null) {
            if (empty($this->qb_set)) {
                return ($this->db_debug) ? $this->display_error('db_must_use_set') : false;
            }
        } else {
            if (empty($set)) {
                return ($this->db_debug) ? $this->display_error('insert_batch() called with no data') : false;
            }

            $this->set_insert_batch($set, '', $escape);
        }

        if (strlen($table) === 0) {
            if (! isset($this->qb_from[0])) {
                return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
            }

            $table = $this->qb_from[0];
        }

        // Batch this baby
        $affected_rows = 0;
        for ($i = 0, $total = count($this->qb_set); $i < $total; $i += $batch_size) {
            if ($this->query($this->_insert_batch($this->protect_identifiers($table, true, $escape, false), $this->qb_keys, array_slice($this->qb_set, $i, $batch_size)))) {
                $affected_rows += $this->affected_rows();
            }
        }

        $this->_reset_write();
        return $affected_rows;
    }

    // --------------------------------------------------------------------

    /**
     * Insert batch statement
     *
     * Generates a platform-specific insert string from the supplied data.
     *
     * @param   string  $table  Table name
     * @param   array   $keys   INSERT keys
     * @param   array   $values INSERT values
     * @return  string
     */
    protected function _insert_batch($table, $keys, $values)
    {
        return 'INSERT INTO ' . $table . ' (' . implode(', ', $keys) . ') VALUES ' . implode(', ', $values);
    }

    // --------------------------------------------------------------------

    /**
     * The "set_insert_batch" function.  Allows key/value pairs to be set for batch inserts
     *
     * @param   mixed
     * @param   string
     * @param   bool
     * @return  CI_DB_query_builder
     */
    public function set_insert_batch($key, $value = '', $escape = null)
    {
        $key = $this->_object_to_array_batch($key);

        if (! is_array($key)) {
            $key = array($key => $value);
        }

        is_bool($escape) or $escape = $this->_protect_identifiers;

        $keys = array_keys($this->_object_to_array(reset($key)));
        sort($keys);

        foreach ($key as $row) {
            $row = $this->_object_to_array($row);
            if (count(array_diff($keys, array_keys($row))) > 0 or count(array_diff(array_keys($row), $keys)) > 0) {
                // batch function above returns an error on an empty array
                $this->qb_set[] = array();
                return;
            }

            ksort($row); // puts $row in the same order as our keys

            if ($escape !== false) {
                $clean = array();
                foreach ($row as $value) {
                    $clean[] = $this->escape($value);
                }

                $row = $clean;
            }

            $this->qb_set[] = '(' . implode(',', $row) . ')';
        }

        foreach ($keys as $k) {
            $this->qb_keys[] = $this->protect_identifiers($k, false, $escape);
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Get INSERT query string
     *
     * Compiles an insert query and returns the sql
     *
     * @param   string  the table to insert into
     * @param   bool    TRUE: reset QB values; FALSE: leave QB values alone
     * @return  string
     */
    public function get_compiled_insert($table = '', $reset = true)
    {
        if ($this->_validate_insert($table) === false) {
            return false;
        }

        $sql = $this->_insert(
            $this->protect_identifiers(
                $this->qb_from[0],
                true,
                null,
                false
            ),
            array_keys($this->qb_set),
            array_values($this->qb_set)
        );

        if ($reset === true) {
            $this->_reset_write();
        }

        return $sql;
    }

    // --------------------------------------------------------------------

    /**
     * Insert
     *
     * Compiles an insert string and runs the query
     *
     * @param   string  the table to insert data into
     * @param   array   an associative array of insert values
     * @param   bool    $escape Whether to escape values and identifiers
     * @return  bool    TRUE on success, FALSE on failure
     */
    public function insert($table = '', $set = null, $escape = null)
    {
        if ($set !== null) {
            $this->set($set, '', $escape);
        }

        if ($this->_validate_insert($table) === false) {
            return false;
        }

        $sql = $this->_insert(
            $this->protect_identifiers(
                $this->qb_from[0],
                true,
                $escape,
                false
            ),
            array_keys($this->qb_set),
            array_values($this->qb_set)
        );

        $this->_reset_write();
        return $this->query($sql);
    }

    // --------------------------------------------------------------------

    /**
     * Validate Insert
     *
     * This method is used by both insert() and get_compiled_insert() to
     * validate that the there data is actually being set and that table
     * has been chosen to be inserted into.
     *
     * @param   string  the table to insert data into
     * @return  string
     */
    protected function _validate_insert($table = '')
    {
        if (count($this->qb_set) === 0) {
            return ($this->db_debug) ? $this->display_error('db_must_use_set') : false;
        }

        if ($table !== '') {
            $this->qb_from[0] = $table;
        } elseif (! isset($this->qb_from[0])) {
            return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
        }

        return true;
    }

    // --------------------------------------------------------------------

    /**
     * Replace
     *
     * Compiles an replace into string and runs the query
     *
     * @param   string  the table to replace data into
     * @param   array   an associative array of insert values
     * @return  bool    TRUE on success, FALSE on failure
     */
    public function replace($table = '', $set = null)
    {
        if ($set !== null) {
            $this->set($set);
        }

        if (count($this->qb_set) === 0) {
            return ($this->db_debug) ? $this->display_error('db_must_use_set') : false;
        }

        if ($table === '') {
            if (! isset($this->qb_from[0])) {
                return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
            }

            $table = $this->qb_from[0];
        }

        $sql = $this->_replace($this->protect_identifiers($table, true, null, false), array_keys($this->qb_set), array_values($this->qb_set));

        $this->_reset_write();
        return $this->query($sql);
    }

    // --------------------------------------------------------------------

    /**
     * Replace statement
     *
     * Generates a platform-specific replace string from the supplied data
     *
     * @param   string  the table name
     * @param   array   the insert keys
     * @param   array   the insert values
     * @return  string
     */
    protected function _replace($table, $keys, $values)
    {
        return 'REPLACE INTO ' . $table . ' (' . implode(', ', $keys) . ') VALUES (' . implode(', ', $values) . ')';
    }

    // --------------------------------------------------------------------

    /**
     * FROM tables
     *
     * Groups tables in FROM clauses if needed, so there is no confusion
     * about operator precedence.
     *
     * Note: This is only used (and overridden) by MySQL and CUBRID.
     *
     * @return  string
     */
    protected function _from_tables()
    {
        return implode(', ', $this->qb_from);
    }

    // --------------------------------------------------------------------

    /**
     * Get UPDATE query string
     *
     * Compiles an update query and returns the sql
     *
     * @param   string  the table to update
     * @param   bool    TRUE: reset QB values; FALSE: leave QB values alone
     * @return  string
     */
    public function get_compiled_update($table = '', $reset = true)
    {
        // Combine any cached components with the current statements
        $this->_merge_cache();

        if ($this->_validate_update($table) === false) {
            return false;
        }

        $sql = $this->_update($this->qb_from[0], $this->qb_set);

        if ($reset === true) {
            $this->_reset_write();
        }

        return $sql;
    }

    // --------------------------------------------------------------------

    /**
     * UPDATE
     *
     * Compiles an update string and runs the query.
     *
     * @param   string  $table
     * @param   array   $set    An associative array of update values
     * @param   mixed   $where
     * @param   int $limit
     * @return  bool    TRUE on success, FALSE on failure
     */
    public function update($table = '', $set = null, $where = null, $limit = null)
    {
        // Combine any cached components with the current statements
        $this->_merge_cache();

        if ($set !== null) {
            $this->set($set);
        }

        if ($this->_validate_update($table) === false) {
            return false;
        }

        if ($where !== null) {
            $this->where($where);
        }

        if (! empty($limit)) {
            $this->limit($limit);
        }

        $sql = $this->_update($this->qb_from[0], $this->qb_set);
        $this->_reset_write();
        return $this->query($sql);
    }

    // --------------------------------------------------------------------

    /**
     * Validate Update
     *
     * This method is used by both update() and get_compiled_update() to
     * validate that data is actually being set and that a table has been
     * chosen to be update.
     *
     * @param   string  the table to update data on
     * @return  bool
     */
    protected function _validate_update($table)
    {
        if (count($this->qb_set) === 0) {
            return ($this->db_debug) ? $this->display_error('db_must_use_set') : false;
        }

        if ($table !== '') {
            $this->qb_from = array($this->protect_identifiers($table, true, null, false));
        } elseif (! isset($this->qb_from[0])) {
            return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
        }

        return true;
    }

    // --------------------------------------------------------------------

    /**
     * Update_Batch
     *
     * Compiles an update string and runs the query
     *
     * @param   string  the table to retrieve the results from
     * @param   array   an associative array of update values
     * @param   string  the where key
     * @return  int number of rows affected or FALSE on failure
     */
    public function update_batch($table, $set = null, $index = null, $batch_size = 100)
    {
        // Combine any cached components with the current statements
        $this->_merge_cache();

        if ($index === null) {
            return ($this->db_debug) ? $this->display_error('db_must_use_index') : false;
        }

        if ($set === null) {
            if (empty($this->qb_set_ub)) {
                return ($this->db_debug) ? $this->display_error('db_must_use_set') : false;
            }
        } else {
            if (empty($set)) {
                return ($this->db_debug) ? $this->display_error('update_batch() called with no data') : false;
            }

            $this->set_update_batch($set, $index);
        }

        if (strlen($table) === 0) {
            if (! isset($this->qb_from[0])) {
                return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
            }

            $table = $this->qb_from[0];
        }

        // Batch this baby
        $affected_rows = 0;
        for ($i = 0, $total = count($this->qb_set_ub); $i < $total; $i += $batch_size) {
            if ($this->query($this->_update_batch($this->protect_identifiers($table, true, null, false), array_slice($this->qb_set_ub, $i, $batch_size), $index))) {
                $affected_rows += $this->affected_rows();
            }

            $this->qb_where = array();
        }

        $this->_reset_write();
        return $affected_rows;
    }

    // --------------------------------------------------------------------

    /**
     * Update_Batch statement
     *
     * Generates a platform-specific batch update string from the supplied data
     *
     * @param   string  $table  Table name
     * @param   array   $values Update data
     * @param   string  $index  WHERE key
     * @return  string
     */
    protected function _update_batch($table, $values, $index)
    {
        $ids = array();
        foreach ($values as $key => $val) {
            $ids[] = $val[$index]['value'];

            foreach (array_keys($val) as $field) {
                if ($field !== $index) {
                    $final[$val[$field]['field']][] = 'WHEN ' . $val[$index]['field'] . ' = ' . $val[$index]['value'] . ' THEN ' . $val[$field]['value'];
                }
            }
        }

        $cases = '';
        foreach ($final as $k => $v) {
            $cases .= $k . " = CASE \n"
                . implode("\n", $v) . "\n"
                . 'ELSE ' . $k . ' END, ';
        }

        $this->where($val[$index]['field'] . ' IN(' . implode(',', $ids) . ')', null, false);

        return 'UPDATE ' . $table . ' SET ' . substr($cases, 0, -2) . $this->_compile_wh('qb_where');
    }

    // --------------------------------------------------------------------

    /**
     * The "set_update_batch" function.  Allows key/value pairs to be set for batch updating
     *
     * @param   array
     * @param   string
     * @param   bool
     * @return  CI_DB_query_builder
     */
    public function set_update_batch($key, $index = '', $escape = null)
    {
        $key = $this->_object_to_array_batch($key);

        if (! is_array($key)) {
            // @todo error
        }

        is_bool($escape) or $escape = $this->_protect_identifiers;

        foreach ($key as $k => $v) {
            $index_set = false;
            $clean = array();
            foreach ($v as $k2 => $v2) {
                if ($k2 === $index) {
                    $index_set = true;
                }

                $clean[$k2] = array(
                    'field'  => $this->protect_identifiers($k2, false, $escape),
                    'value'  => ($escape === false ? $v2 : $this->escape($v2))
                );
            }

            if ($index_set === false) {
                return $this->display_error('db_batch_missing_index');
            }

            $this->qb_set_ub[] = $clean;
        }

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Empty Table
     *
     * Compiles a delete string and runs "DELETE FROM table"
     *
     * @param   string  the table to empty
     * @return  bool    TRUE on success, FALSE on failure
     */
    public function empty_table($table = '')
    {
        if ($table === '') {
            if (! isset($this->qb_from[0])) {
                return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
            }

            $table = $this->qb_from[0];
        } else {
            $table = $this->protect_identifiers($table, true, null, false);
        }

        $sql = $this->_delete($table);
        $this->_reset_write();
        return $this->query($sql);
    }

    // --------------------------------------------------------------------

    /**
     * Truncate
     *
     * Compiles a truncate string and runs the query
     * If the database does not support the truncate() command
     * This function maps to "DELETE FROM table"
     *
     * @param   string  the table to truncate
     * @return  bool    TRUE on success, FALSE on failure
     */
    public function truncate($table = '')
    {
        if ($table === '') {
            if (! isset($this->qb_from[0])) {
                return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
            }

            $table = $this->qb_from[0];
        } else {
            $table = $this->protect_identifiers($table, true, null, false);
        }

        $sql = $this->_truncate($table);
        $this->_reset_write();
        return $this->query($sql);
    }

    // --------------------------------------------------------------------

    /**
     * Truncate statement
     *
     * Generates a platform-specific truncate string from the supplied data
     *
     * If the database does not support the truncate() command,
     * then this method maps to 'DELETE FROM table'
     *
     * @param   string  the table name
     * @return  string
     */
    protected function _truncate($table)
    {
        return 'TRUNCATE ' . $table;
    }

    // --------------------------------------------------------------------

    /**
     * Get DELETE query string
     *
     * Compiles a delete query string and returns the sql
     *
     * @param   string  the table to delete from
     * @param   bool    TRUE: reset QB values; FALSE: leave QB values alone
     * @return  string
     */
    public function get_compiled_delete($table = '', $reset = true)
    {
        $this->return_delete_sql = true;
        $sql = $this->delete($table, '', null, $reset);
        $this->return_delete_sql = false;
        return $sql;
    }

    // --------------------------------------------------------------------

    /**
     * Delete
     *
     * Compiles a delete string and runs the query
     *
     * @param   mixed   the table(s) to delete from. String or array
     * @param   mixed   the where clause
     * @param   mixed   the limit clause
     * @param   bool
     * @return  mixed
     */
    public function delete($table = '', $where = '', $limit = null, $reset_data = true)
    {
        // Combine any cached components with the current statements
        $this->_merge_cache();

        if ($table === '') {
            if (! isset($this->qb_from[0])) {
                return ($this->db_debug) ? $this->display_error('db_must_set_table') : false;
            }

            $table = $this->qb_from[0];
        } elseif (is_array($table)) {
            empty($where) && $reset_data = false;

            foreach ($table as $single_table) {
                $this->delete($single_table, $where, $limit, $reset_data);
            }

            return;
        } else {
            $table = $this->protect_identifiers($table, true, null, false);
        }

        if ($where !== '') {
            $this->where($where);
        }

        if (! empty($limit)) {
            $this->limit($limit);
        }

        if (count($this->qb_where) === 0) {
            return ($this->db_debug) ? $this->display_error('db_del_must_use_where') : false;
        }

        $sql = $this->_delete($table);
        if ($reset_data) {
            $this->_reset_write();
        }

        return ($this->return_delete_sql === true) ? $sql : $this->query($sql);
    }

    // --------------------------------------------------------------------

    /**
     * Delete statement
     *
     * Generates a platform-specific delete string from the supplied data
     *
     * @param   string  the table name
     * @return  string
     */
    protected function _delete($table)
    {
        return 'DELETE FROM ' . $table . $this->_compile_wh('qb_where')
            . ($this->qb_limit !== false ? ' LIMIT ' . $this->qb_limit : '');
    }

    // --------------------------------------------------------------------

    /**
     * DB Prefix
     *
     * Prepends a database prefix if one exists in configuration
     *
     * @param   string  the table
     * @return  string
     */
    public function dbprefix($table = '')
    {
        if ($table === '') {
            $this->display_error('db_table_name_required');
        }

        return $this->dbprefix . $table;
    }

    // --------------------------------------------------------------------

    /**
     * Set DB Prefix
     *
     * Set's the DB Prefix to something new without needing to reconnect
     *
     * @param   string  the prefix
     * @return  string
     */
    public function set_dbprefix($prefix = '')
    {
        return $this->dbprefix = $prefix;
    }

    // --------------------------------------------------------------------

    /**
     * Track Aliases
     *
     * Used to track SQL statements written with aliased tables.
     *
     * @param   string  The table to inspect
     * @return  string
     */
    protected function _track_aliases($table)
    {
        if (is_array($table)) {
            foreach ($table as $t) {
                $this->_track_aliases($t);
            }
            return;
        }

        // Does the string contain a comma?  If so, we need to separate
        // the string into discreet statements
        if (strpos($table, ',') !== false) {
            return $this->_track_aliases(explode(',', $table));
        }

        // if a table alias is used we can recognize it by a space
        if (strpos($table, ' ') !== false) {
            // if the alias is written with the AS keyword, remove it
            $table = preg_replace('/\s+AS\s+/i', ' ', $table);

            // Grab the alias
            $table = trim(strrchr($table, ' '));

            // Store the alias, if it doesn't already exist
            if (! in_array($table, $this->qb_aliased_tables, true)) {
                $this->qb_aliased_tables[] = $table;
                if ($this->qb_caching === true && ! in_array($table, $this->qb_cache_aliased_tables, true)) {
                    $this->qb_cache_aliased_tables[] = $table;
                    $this->qb_cache_exists[] = 'aliased_tables';
                }
            }
        }
    }

    // --------------------------------------------------------------------

    /**
     * Compile the SELECT statement
     *
     * Generates a query string based on which functions were used.
     * Should not be called directly.
     *
     * @param   bool    $select_override
     * @return  string
     */
    protected function _compile_select($select_override = false)
    {
        // Combine any cached components with the current statements
        $this->_merge_cache();

        // Write the "select" portion of the query
        if ($select_override !== false) {
            $sql = $select_override;
        } else {
            $sql = (! $this->qb_distinct) ? 'SELECT ' : 'SELECT DISTINCT ';

            if (count($this->qb_select) === 0) {
                $sql .= '*';
            } else {
                // Cycle through the "select" portion of the query and prep each column name.
                // The reason we protect identifiers here rather than in the select() function
                // is because until the user calls the from() function we don't know if there are aliases
                foreach ($this->qb_select as $key => $val) {
                    $no_escape = isset($this->qb_no_escape[$key]) ? $this->qb_no_escape[$key] : null;
                    $this->qb_select[$key] = $this->protect_identifiers($val, false, $no_escape);
                }

                $sql .= implode(', ', $this->qb_select);
            }
        }

        // Write the "FROM" portion of the query
        if (count($this->qb_from) > 0) {
            $sql .= "\nFROM " . $this->_from_tables();
        }

        // Write the "JOIN" portion of the query
        if (count($this->qb_join) > 0) {
            $sql .= "\n" . implode("\n", $this->qb_join);
        }

        $sql .= $this->_compile_wh('qb_where')
            . $this->_compile_group_by()
            . $this->_compile_wh('qb_having')
            . $this->_compile_order_by(); // ORDER BY

        // LIMIT
        if ($this->qb_limit !== false or $this->qb_offset) {
            return $this->_limit($sql . "\n");
        }

        return $sql;
    }

    // --------------------------------------------------------------------

    /**
     * Compile WHERE, HAVING statements
     *
     * Escapes identifiers in WHERE and HAVING statements at execution time.
     *
     * Required so that aliases are tracked properly, regardless of whether
     * where(), or_where(), having(), or_having are called prior to from(),
     * join() and dbprefix is added only if needed.
     *
     * @param   string  $qb_key 'qb_where' or 'qb_having'
     * @return  string  SQL statement
     */
    protected function _compile_wh($qb_key)
    {
        if (count($this->$qb_key) > 0) {
            for ($i = 0, $c = count($this->$qb_key); $i < $c; $i++) {
                // Is this condition already compiled?
                if (is_string($this->{$qb_key}[$i])) {
                    continue;
                } elseif ($this->{$qb_key}[$i]['escape'] === false) {
                    $this->{$qb_key}[$i] = $this->{$qb_key}[$i]['condition'] . (isset($this->{$qb_key}[$i]['value']) ? ' ' . $this->{$qb_key}[$i]['value'] : '');
                    continue;
                }

                // Split multiple conditions
                $conditions = preg_split(
                    '/((?:^|\s+)AND\s+|(?:^|\s+)OR\s+)/i',
                    $this->{$qb_key}[$i]['condition'],
                    -1,
                    PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY
                );

                for ($ci = 0, $cc = count($conditions); $ci < $cc; $ci++) {
                    if (
                        ($op = $this->_get_operator($conditions[$ci])) === false
                        or ! preg_match('/^(\(?)(.*)(' . preg_quote($op, '/') . ')\s*(.*(?<!\)))?(\)?)$/i', $conditions[$ci], $matches)
                    ) {
                        continue;
                    }

                    // $matches = array(
                    //  0 => '(test <= foo)',   /* the whole thing */
                    //  1 => '(',       /* optional */
                    //  2 => 'test',        /* the field name */
                    //  3 => ' <= ',        /* $op */
                    //  4 => 'foo',     /* optional, if $op is e.g. 'IS NULL' */
                    //  5 => ')'        /* optional */
                    // );

                    if (! empty($matches[4])) {
                        $this->_is_literal($matches[4]) or $matches[4] = $this->protect_identifiers(trim($matches[4]));
                        $matches[4] = ' ' . $matches[4];
                    }

                    $conditions[$ci] = $matches[1] . $this->protect_identifiers(trim($matches[2]))
                        . ' ' . trim($matches[3]) . $matches[4] . $matches[5];
                }

                $this->{$qb_key}[$i] = implode('', $conditions) . (isset($this->{$qb_key}[$i]['value']) ? ' ' . $this->{$qb_key}[$i]['value'] : '');
            }

            return ($qb_key === 'qb_having' ? "\nHAVING " : "\nWHERE ")
                . implode("\n", $this->$qb_key);
        }

        return '';
    }

    // --------------------------------------------------------------------

    /**
     * Compile GROUP BY
     *
     * Escapes identifiers in GROUP BY statements at execution time.
     *
     * Required so that aliases are tracked properly, regardless of whether
     * group_by() is called prior to from(), join() and dbprefix is added
     * only if needed.
     *
     * @return  string  SQL statement
     */
    protected function _compile_group_by()
    {
        if (count($this->qb_groupby) > 0) {
            for ($i = 0, $c = count($this->qb_groupby); $i < $c; $i++) {
                // Is it already compiled?
                if (is_string($this->qb_groupby[$i])) {
                    continue;
                }

                $this->qb_groupby[$i] = ($this->qb_groupby[$i]['escape'] === false or $this->_is_literal($this->qb_groupby[$i]['field']))
                    ? $this->qb_groupby[$i]['field']
                    : $this->protect_identifiers($this->qb_groupby[$i]['field']);
            }

            return "\nGROUP BY " . implode(', ', $this->qb_groupby);
        }

        return '';
    }

    // --------------------------------------------------------------------

    /**
     * Compile ORDER BY
     *
     * Escapes identifiers in ORDER BY statements at execution time.
     *
     * Required so that aliases are tracked properly, regardless of whether
     * order_by() is called prior to from(), join() and dbprefix is added
     * only if needed.
     *
     * @return  string  SQL statement
     */
    protected function _compile_order_by()
    {
        if (empty($this->qb_orderby)) {
            return '';
        }

        for ($i = 0, $c = count($this->qb_orderby); $i < $c; $i++) {
            if (is_string($this->qb_orderby[$i])) {
                continue;
            }

            if ($this->qb_orderby[$i]['escape'] !== false && ! $this->_is_literal($this->qb_orderby[$i]['field'])) {
                $this->qb_orderby[$i]['field'] = $this->protect_identifiers($this->qb_orderby[$i]['field']);
            }

            $this->qb_orderby[$i] = $this->qb_orderby[$i]['field'] . $this->qb_orderby[$i]['direction'];
        }

        return "\nORDER BY " . implode(', ', $this->qb_orderby);
    }

    // --------------------------------------------------------------------

    /**
     * Object to Array
     *
     * Takes an object as input and converts the class variables to array key/vals
     *
     * @param   object
     * @return  array
     */
    protected function _object_to_array($object)
    {
        if (! is_object($object)) {
            return $object;
        }

        $array = array();
        foreach (get_object_vars($object) as $key => $val) {
            // There are some built in keys we need to ignore for this conversion
            if (! is_object($val) && ! is_array($val) && $key !== '_parent_name') {
                $array[$key] = $val;
            }
        }

        return $array;
    }

    // --------------------------------------------------------------------

    /**
     * Object to Array
     *
     * Takes an object as input and converts the class variables to array key/vals
     *
     * @param   object
     * @return  array
     */
    protected function _object_to_array_batch($object)
    {
        if (! is_object($object)) {
            return $object;
        }

        $array = array();
        $out = get_object_vars($object);
        $fields = array_keys($out);

        foreach ($fields as $val) {
            // There are some built in keys we need to ignore for this conversion
            if ($val !== '_parent_name') {
                $i = 0;
                foreach ($out[$val] as $data) {
                    $array[$i++][$val] = $data;
                }
            }
        }

        return $array;
    }

    // --------------------------------------------------------------------

    /**
     * Start Cache
     *
     * Starts QB caching
     *
     * @return  CI_DB_query_builder
     */
    public function start_cache()
    {
        $this->qb_caching = true;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Stop Cache
     *
     * Stops QB caching
     *
     * @return  CI_DB_query_builder
     */
    public function stop_cache()
    {
        $this->qb_caching = false;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Flush Cache
     *
     * Empties the QB cache
     *
     * @return  CI_DB_query_builder
     */
    public function flush_cache()
    {
        $this->_reset_run(array(
            'qb_cache_select'       => array(),
            'qb_cache_from'         => array(),
            'qb_cache_join'         => array(),
            'qb_cache_where'        => array(),
            'qb_cache_groupby'      => array(),
            'qb_cache_having'       => array(),
            'qb_cache_orderby'      => array(),
            'qb_cache_set'          => array(),
            'qb_cache_exists'       => array(),
            'qb_cache_no_escape'    => array(),
            'qb_cache_aliased_tables'   => array()
        ));

        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Merge Cache
     *
     * When called, this function merges any cached QB arrays with
     * locally called ones.
     *
     * @return  void
     */
    protected function _merge_cache()
    {
        if (count($this->qb_cache_exists) === 0) {
            return;
        } elseif (in_array('select', $this->qb_cache_exists, true)) {
            $qb_no_escape = $this->qb_cache_no_escape;
        }

        foreach (array_unique($this->qb_cache_exists) as $val) { // select, from, etc.
            $qb_variable    = 'qb_' . $val;
            $qb_cache_var   = 'qb_cache_' . $val;
            $qb_new     = $this->$qb_cache_var;

            for ($i = 0, $c = count($this->$qb_variable); $i < $c; $i++) {
                if (! in_array($this->{$qb_variable}[$i], $qb_new, true)) {
                    $qb_new[] = $this->{$qb_variable}[$i];
                    if ($val === 'select') {
                        $qb_no_escape[] = $this->qb_no_escape[$i];
                    }
                }
            }

            $this->$qb_variable = $qb_new;
            if ($val === 'select') {
                $this->qb_no_escape = $qb_no_escape;
            }
        }
    }

    // --------------------------------------------------------------------

    /**
     * Is literal
     *
     * Determines if a string represents a literal value or a field name
     *
     * @param   string  $str
     * @return  bool
     */
    protected function _is_literal($str)
    {
        $str = trim($str);

        if (empty($str) or ctype_digit($str) or (string) (float) $str === $str or in_array(strtoupper($str), array('TRUE', 'FALSE'), true)) {
            return true;
        }

        static $_str;

        if (empty($_str)) {
            $_str = ($this->_escape_char !== '"')
                ? array('"', "'") : array("'");
        }

        return in_array($str[0], $_str, true);
    }

    // --------------------------------------------------------------------

    /**
     * Reset Query Builder values.
     *
     * Publicly-visible method to reset the QB values.
     *
     * @return  CI_DB_query_builder
     */
    public function reset_query()
    {
        $this->_reset_select();
        $this->_reset_write();
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Resets the query builder values.  Called by the get() function
     *
     * @param   array   An array of fields to reset
     * @return  void
     */
    protected function _reset_run($qb_reset_items)
    {
        foreach ($qb_reset_items as $item => $default_value) {
            $this->$item = $default_value;
        }
    }

    // --------------------------------------------------------------------

    /**
     * Resets the query builder values.  Called by the get() function
     *
     * @return  void
     */
    protected function _reset_select()
    {
        $this->_reset_run(array(
            'qb_select'     => array(),
            'qb_from'       => array(),
            'qb_join'       => array(),
            'qb_where'      => array(),
            'qb_groupby'        => array(),
            'qb_having'     => array(),
            'qb_orderby'        => array(),
            'qb_aliased_tables' => array(),
            'qb_no_escape'      => array(),
            'qb_distinct'       => false,
            'qb_limit'      => false,
            'qb_offset'     => false
        ));
    }

    // --------------------------------------------------------------------

    /**
     * Resets the query builder "write" values.
     *
     * Called by the insert() update() insert_batch() update_batch() and delete() functions
     *
     * @return  void
     */
    protected function _reset_write()
    {
        $this->_reset_run(array(
            'qb_set'    => array(),
            'qb_set_ub' => array(),
            'qb_from'   => array(),
            'qb_join'   => array(),
            'qb_where'  => array(),
            'qb_orderby'    => array(),
            'qb_keys'   => array(),
            'qb_limit'  => false
        ));
    }
}