function dropColumnDefault($table, $column)
{
$f_schema = $this->_schema;
$this->fieldClean($f_schema);
$this->fieldClean($table);
$this->fieldClean($column);
$sql = "ALTER TABLE \"{$f_schema}\".\"{$table}\" ALTER COLUMN \"{$column}\" DROP DEFAULT";
return $this->execute($sql);
}