小编Rus*_* K.的帖子

这段代码工作正常:

select fk, max(case when 1 = 0 then 1 else null end) maxx
    from (values(1, null), (1, null)) x(fk, a) 
    group by fk;

输出:

fk          maxx
----------- -----------
1           NULL

有:

Warning: Null value is eliminated by an aggregate or other SET operation.

但是这段代码:

select fk, max(a) maxx
    from (values(1, null), (1, null)) x(fk, a)
    group by fk;

给出错误:

Msg 8117, Level 16, State 1, Line 5 Operand data type NULL is invalid for max operator.

在这两种情况下sql server计算max …