刚发现的,请大家不要运行下面语句,看得出的结果应该是什么?为什么结果是那样?
create table a(ss varchar(10))
goinsert into a
select 'a'
union all
select 'b'
union all
select 'c'
union all
select 'd'create table b(ss varchar(10))
goinsert into b
select 'b'
union all
select 'c'
union all
select 'd'
union all
select 'e'
union all
select nullselect * from a
where ss not in(select ss from b)
create table a(ss varchar(10))
goinsert into a
select 'a'
union all
select 'b'
union all
select 'c'
union all
select 'd'create table b(ss varchar(10))
goinsert into b
select 'b'
union all
select 'c'
union all
select 'd'
union all
select 'e'
union all
select nullselect * from a
where ss not in(select ss from b)
a<> 1 and a <>2 and a<>null --这个为假,条件永远为假所以没有
a<>null 为null
true and null 为null
where 视null为false