sql case when

[lbph1]

select case sum(f_amount) when null then 0 else sum(f_amount) end as f_amount1 from cc_SaleQuoteFee where FID = 4560
为什么结果还是null，而不是0？？？？？

[水族杰纶]

select case sum(f_amount) when null then 0 else isnull(sum(f_amount),0) end as f_amount1 from cc_SaleQuoteFee where FID = 4560

[lgxyz]

select  sum(isnull(f_amount,0)) as f_amount1 from cc_SaleQuoteFee where FID = 4560 

[-狙击手-]

select sum(isnull(f_amount,0)) as f_amount1
from cc_SaleQuoteFee
where FID = 4560

[g_lbz]

select  case  when sum(f_amount) is null then 0 else  sum(f_amount) end as f_amount1 
from cc_SaleQuoteFee
 where FID = 4560 

[ysai]

case x when null 就是判断 x = null 成立与否
可sql的定义为:任何值与null比较,得出的结果都是null
所以,when null没有任何意义

null值只能用以下方式处理
x is null
isnull(x, 默认值)

[让你望见影子的墙]

select sum(isnull(f_amount,0)) as f_amount1 from cc_SaleQuoteFee where FID = 4560

空值的判断使用is null或者is not null