$sql = "ALTER TABLE $table ADD COLUMN " . $this->_columnSql($columndef);
$res = $this->conn->query($sql);
$sql = "ALTER TABLE $table ADD COLUMN " . $this->_columnSql($columndef);
$res = $this->conn->query($sql);
$sql = "ALTER TABLE $table MODIFY COLUMN " .
$this->_columnSql($columndef);
$res = $this->conn->query($sql);
$sql = "ALTER TABLE $table MODIFY COLUMN " .
$this->_columnSql($columndef);
$res = $this->conn->query($sql);