tsql : is it possible to do nested case statements in a select?

Question

如何将嵌套的 if 语句合并到 sql 查询的 select 子句中？ 我知道在条件 then X else y 结束时使用 case，但是如何以相同的方式为记录集中的每条记录执行嵌套操作。

if x.boy is not null then 
   x.boy 
else if x.girl is not null
   then x.girl 
else if x.dog is not null 
   then x.dog
else 
    x.cat 

这是我的尝试:

SELECT top 10
        id,
        case when x.boy <> NULL then 
            x.boy
        else case when  x.girl <> NULL 
            x.girl
                else case when  x.dog <> NULL 
            x.dog
                else x.cat 

        end as Who 
from house x

这是正确的吗？

Answer 1

是的。案中案并没有什么问题。

尽管如此，这是您正确编写的脚本:

SELECT top 10
    id,
    case
        when x.boy IS NOT NULL then x.boy
        else case
            when x.girl IS NOT NULL THEN x.girl
            else case
                when x.dog IS NOT NULL THEN x.dog
                else x.cat
            end
        end
    end as Who 
from house x

或者

SELECT top 10
    id,
    case
        when x.boy IS NOT NULL then x.boy
        when x.girl IS NOT NULL THEN x.girl
        when x.dog IS NOT NULL THEN x.dog
        else x.cat
    end as Who 
from house x

或者

SELECT top 10
    id,
    coalesce(x.boy, x.girl, x.dog, x.cat) AS Who
from house x