Ok... I make it in PHP...
function alter_table($table_name, $column_name, $column_type) {
$result = mysql_query("SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = `$table_name` AND COLUMN_NAME = `$column_name`");
if(!$result) {
mysql_query("ALTER TABLE `$table_name`
ADD COLUMN `$column_name` $column_type");
}
}