code: public function addDefaultValue($name, $table, $column, $value)
      {
          return 'ALTER TABLE ' . $this->db->quoteTableName($table) . ' ADD CONSTRAINT '
              . $this->db->quoteColumnName($name) . ' DEFAULT ' . $this->db->quoteValue($value) . ' FOR '
              . $this->db->quoteColumnName($column);
      }
docs: {@inheritdoc}