select * from a where ''='';
select * from a where ''=null;
select * from a where ''is null;
select * from a where null is '';
select * from a where null ='';
select * from a where null is null;
上面哪一个SQL语句有返回值。
欢迎大家踊跃讨论.
select * from a where ''=null;
select * from a where ''is null;
select * from a where null is '';
select * from a where null ='';
select * from a where null is null;
上面哪一个SQL语句有返回值。
欢迎大家踊跃讨论.
有返回值了,判断为空的写法只能是is null, oracle里空可以写成''和null,所以只有这两个对
select * from a where ''is null;
select * from a where null is null;
第四条应该不成立;
既然是考纯sql,应该和数据库厂商无关的。
select * from a where null is null;
create table a
(
column1 varchar2(256)
)insert into a values('1');
select * from a where ''='';
无返回记录select * from a where ''=null;
无返回记录select * from a where ''is null;
返回记录select * from a where null is '';
语法错误select * from a where null ='';
无返回记录select * from a where null is null;
返回记录
select * from a where ''is null;
select * from a where ''is null;