/**
* DBMS-specific implementation for setting a column's default value
**/
protected function _setDefault()
{
if ($this->_default === null) {
$this->_table->alter(sprintf('ALTER COLUMN %s DROP DEFAULT', $this->_database->prepareIdentifier($this->_name)));
} else {
$this->_table->alter(sprintf('ALTER COLUMN %s SET DEFAULT %s', $this->_database->prepareIdentifier($this->_name), $this->_database->prepareValue($this->_default, $this->_datatype)));
}
}