在中若删除表中一个不存在的字段,如 “alter table test drop column xxx”,则会提示:

ORA-00904:”xxx”:标识符无效

若在程序中执行该语句则会报异常,这就需要我们在删除字段前先判断该字段是否存在,若存在则删除.

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;