Question

这个SQL语句怎么写。。。求助大神

有一张表T
-------
A | B
-------
null| 1
null| 2
null| 3
null| null

我想查符合条件：
1.B=‘3’并且A为null
2.A、 B都为null
的记录条数用SQL怎么写。。急。。。

快速答对的并且通过编译的分不是问题。。跪求
谢谢大家，大家都对，我脑子一时糊了。

Answer 1

select count(1) as ct from t where t.b='3' and t.a is null
union
select count(1) as ct from t where t.a is null and t.b is null
如果要求和，就加一下:
select sum(a.ct) from
(select count(1) as ct from t where t.b='3' and t.a is null
union
select count(1) as ct from t where t.a is null and t.b is null
) a

还有更简单的：
select count(1) from t where t.a is null and (t.b='3' or t.b is null)

Answer 2

select * from t where b=3 and a=null or a=null and b=null

你是这个意思吗，一条查出来。你先试试这么写。

Answer 3

select * from T where (B='3' and A is null) or (B is null and A is null)