在Oracle中若刪除表中一個不存在的欄位,如 “alter table test drop column xxx”,則會提示:

ORA-00904:”xxx”:識別符號無效

若在程式中執行該語句則會報異常,這就需要我們在刪除欄位前先判斷該欄位是否存在,若存在則刪除.

DECLARE
  num NUMBER;
BEGIN
  SELECT COUNT(1)
    INTO num
    from cols
   where table_name = upper('tableName')
     and column_name = upper('columnName');
  IF num > 0 THEN
      execute immediate 'alter
 
 table tableName drop column columnName';
  END IF;
END;