/wp-admin/install-helper.php

<?php
$wp_only_load_config = true;
require_once(dirname(dirname(__FILE__)).'/wp-load.php');
$debug = 0;

/**
 ** maybe_create_table()
 ** Create db table if it doesn't exist.
 ** Returns:  true if already exists or on successful completion
 **           false on error
 */
if ( ! function_exists('maybe_create_table') ) :
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;

/**
 ** maybe_add_column()
 ** Add column to db table if it doesn't exist.
 ** Returns:  true if already exists or on successful completion
 **           false on error
 */
if ( ! function_exists('maybe_add_column') ) :
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;

/**
 ** maybe_drop_column()
 ** Drop column from db table if it exists.
 ** Returns:  true if it doesn't already exist or on successful drop
 **           false on error
 */
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()
 ** Check column matches passed in criteria.
 ** Pass in null to skip checking that criteria
 ** Returns:  true if it matches
 **           false otherwise
 ** (case sensitive) Column names returned from DESC table are:
 **      Field
 **      Type
 **      Null
 **      Key
 **      Default
 **      Extra
 */
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;
}

/*
echo "<p>testing</p>";
echo "<pre>";

//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;
}
echo "</pre>";
*/
?>