mysql - 如何通过包含空值来编写查询

Question

我有一个疑问

SELECT sum(cash)  from bought_cash WHERE uid=1 AND source NOT IN ('a', 'b')  

给出的结果为140

和

 SELECT sum(cash)  from bought_cash WHERE uid=1 AND source  IN ('a', 'b')  

给出NULL

和

SELECT sum(cash)  from bought_cash WHERE uid=1 

给出的结果为240

和

SELECT sum(cash)  from bought_cash WHERE uid=1 and source is null  

给出的结果为100

如何编写查询，以便第一个查询通过包含空值给出 240 结果。

Answer 1

接下来您也可以尝试:

select sum(cash) 
from bought_cash
where uid = 1 and (source is null or source not in ('a', 'b'))