source: trunk/www.guidonia.net/wp/wp-admin/install-helper.php@ 44

<?php
/**
 * Plugins may load this file to gain access to special helper functions for
 * plugin installation. This file is not included by WordPress and it is
 * recommended, to prevent fatal errors, that this file is included using
 * require_once().
 *
 * These functions are not optimized for speed, but they should only be used
 * once in a while, so speed shouldn't be a concern. If it is and you are
 * needing to use these functions a lot, you might experience time outs. If you
 * do, then it is advised to just write the SQL code yourself.
 *
 * You can turn debugging on, by setting $debug to 1 after you include this
 * file.
 *
 * <code>
 * check_column('wp_links', 'link_description', 'mediumtext');
 * if (check_column($wpdb->comments, 'comment_author', 'tinytext'))
 *     echo "ok\n";
 *
 * $error_count = 0;
 * $tablename = $wpdb->links;
 * // check the column
 * if (!check_column($wpdb->links, 'link_description', 'varchar(255)')) {
 *     $ddl = "ALTER TABLE $wpdb->links MODIFY COLUMN link_description varchar(255) NOT NULL DEFAULT '' ";
 *     $q = $wpdb->query($ddl);
 * }
 *
 * if (check_column($wpdb->links, 'link_description', 'varchar(255)')) {
 *     $res .= $tablename . ' - ok <br />';
 * } else {
 *     $res .= 'There was a problem with ' . $tablename . '<br />';
 *     ++$error_count;
 * }
 * </code>
 *
 * @package WordPress
 * @subpackage Plugin
 */

/**
 * @global bool $wp_only_load_config
 * @name $wp_only_load_config
 * @var bool
 * @since unknown
 */
$wp_only_load_config = true;

/** Load WordPress Bootstrap */
require_once(dirname(dirname(__FILE__)).'/wp-load.php');

/**
 * Turn debugging on or off.
 * @global bool|int $debug
 * @name $debug
 * @var bool|int
 * @since unknown
 */
$debug = 0;

if ( ! function_exists('maybe_create_table') ) :
/**
 * Create database table, if it doesn't already exist.
 *
 * @since unknown
 * @package WordPress
 * @subpackage Plugin
 * @uses $wpdb
 *
 * @param string $table_name Database table name.
 * @param string $create_ddl Create database table SQL.
 * @return bool False on error, true if already exists or success.
 */
function maybe_create_table($table_name, $create_ddl) {
        global $wpdb;
        foreach ($wpdb->get_col("SHOW TABLES",0) as $table ) {
                if ($table == $table_name) {
                        return true;
                }
        }
        //didn't find it try to create it.
        $wpdb->query($create_ddl);
        // we cannot directly tell that whether this succeeded!
        foreach ($wpdb->get_col("SHOW TABLES",0) as $table ) {
                if ($table == $table_name) {
                        return true;
                }
        }
        return false;
}
endif;

if ( ! function_exists('maybe_add_column') ) :
/**
 * Add column to database table, if column doesn't already exist in table.
 *
 * @since unknown
 * @package WordPress
 * @subpackage Plugin
 * @uses $wpdb
 * @uses $debug
 *
 * @param string $table_name Database table name
 * @param string $column_name Table column name
 * @param string $create_ddl SQL to add column to table.
 * @return bool False on failure. True, if already exists or was successful.
 */
function maybe_add_column($table_name, $column_name, $create_ddl) {
        global $wpdb, $debug;
        foreach ($wpdb->get_col("DESC $table_name",0) as $column ) {
                if ($debug) echo("checking $column == $column_name<br />");

                if ($column == $column_name) {
                        return true;
                }
        }
        //didn't find it try to create it.
        $wpdb->query($create_ddl);
        // we cannot directly tell that whether this succeeded!
        foreach ($wpdb->get_col("DESC $table_name",0) as $column ) {
                if ($column == $column_name) {
                        return true;
                }
        }
        return false;
}
endif;

/**
 * Drop column from database table, if it exists.
 *
 * @since unknown
 * @package WordPress
 * @subpackage Plugin
 * @uses $wpdb
 *
 * @param string $table_name Table name
 * @param string $column_name Column name
 * @param string $drop_ddl SQL statement to drop column.
 * @return bool False on failure, true on success or doesn't exist.
 */
function maybe_drop_column($table_name, $column_name, $drop_ddl) {
        global $wpdb;
        foreach ($wpdb->get_col("DESC $table_name",0) as $column ) {
                if ($column == $column_name) {
                        //found it try to drop it.
                        $wpdb->query($drop_ddl);
                        // we cannot directly tell that whether this succeeded!
                        foreach ($wpdb->get_col("DESC $table_name",0) as $column ) {
                                if ($column == $column_name) {
                                        return false;
                                }
                        }
                }
        }
        // else didn't find it
        return true;
}

/**
 * Check column matches criteria.
 *
 * Uses the SQL DESC for retrieving the table info for the column. It will help
 * understand the parameters, if you do more research on what column information
 * is returned by the SQL statement. Pass in null to skip checking that
 * criteria.
 *
 * Column names returned from DESC table are case sensitive and are listed:
 *      Field
 *      Type
 *      Null
 *      Key
 *      Default
 *      Extra
 *
 * @since unknown
 * @package WordPress
 * @subpackage Plugin
 *
 * @param string $table_name Table name
 * @param string $col_name Column name
 * @param string $col_type Column type
 * @param bool $is_null Optional. Check is null.
 * @param mixed $key Optional. Key info.
 * @param mixed $default Optional. Default value.
 * @param mixed $extra Optional. Extra value.
 * @return bool True, if matches. False, if not matching.
 */
function check_column($table_name, $col_name, $col_type, $is_null = null, $key = null, $default = null, $extra = null) {
        global $wpdb, $debug;
        $diffs = 0;
        $results = $wpdb->get_results("DESC $table_name");

        foreach ($results as $row ) {
                if ($debug > 1) print_r($row);

                if ($row->Field == $col_name) {
                        // got our column, check the params
                        if ($debug) echo ("checking $row->Type against $col_type\n");
                        if (($col_type != null) && ($row->Type != $col_type)) {
                                ++$diffs;
                        }
                        if (($is_null != null) && ($row->Null != $is_null)) {
                                ++$diffs;
                        }
                        if (($key != null) && ($row->Key  != $key)) {
                                ++$diffs;
                        }
                        if (($default != null) && ($row->Default != $default)) {
                                ++$diffs;
                        }
                        if (($extra != null) && ($row->Extra != $extra)) {
                                ++$diffs;
                        }
                        if ($diffs > 0) {
                                if ($debug) echo ("diffs = $diffs returning false\n");
                                return false;
                        }
                        return true;
                } // end if found our column
        }
        return false;
}

?>