在Oracle中若删除一个不存在的表,如 “DROP TABLE tableName”,则会提示:

ORA-00942:表或视图不存在

若在程序中执行该语句则会报异常,这就需要我们在删除表前先判断该表是否存在,若存在则删除.

DECLARE num NUMBER; BEGIN SELECT COUNT(1) INTO num FROM USER_TABLES WHERE TABLE_NAME = UPPER('tableName'); IF num > 0 THEN EXECUTE IMMEDIATE 'DROP TABLE tableName'; END IF; END;

在Oracle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;