Function to merge new SQL argument arrays (right) with defaults (left)

function-array_merge_for_sql.php

<?php

/**
 * Merges new SQL argument arrays with defaults
 *
 * Differs from {@link array_merge()} and {@link array_merge_recursive()}:
 *
 * 1. Array of 'where', 'orderby', 'groupby' and 'join' keys should be
 *    appended and remain unique.
 * 2. 'select', 'limit' should be overwritten, by new argument on right
 *
 * Left key's values are appended to the end of key's value (important for
 * `ORDER BY` priority).
 *
 * @param   array   $old    Left array to merge into
 * @param   array   $new    Right array to be merged into left
 * @returns array           Result of merge
 * @author                  Martin Adamko <@martin_adamko>
 * @license                 The MIT license <http://opensource.org/licenses/MIT>
 *
 */
function array_merge_for_sql(array $old, array $new)
{
    static $multiple = array('where', 'orderby', 'groupby', 'join');

    // Default merge: overwrites old values with new values
    $out = array_merge($old, $new);

    // Fix removal of old entries, appended at the end
    foreach ($out as $k => &$v) {
        if (in_array($k, $multiple)) {
            $out[$k] = (array) $out[$k];

            if (isset($old[$k])) {
                $old[$k] = (array) $old[$k];
                foreach ($old[$k] as $condition) {
                    if(!in_array($condition, $out[$k])) {
                        $out[$k][] = $condition;
                    }
                }
            }
        } elseif (is_array($out[$k])) {
            reset($out[$k]);
            $out[$k] = current($out[$k]);
        }
    }

    return $out;
}