Question

如何在SQL查询的select子句中包含嵌套的if语句？我知道使用case时条件然后X else y结束但是你如何以相同的方式为记录集中的每个记录做一个嵌套的。

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。案件中的案件没有任何问题。

虽然这是你的脚本，但是写得很好：

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

OR

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

OR

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

Answer 2

您可以使用COALESCE简化此操作。

SELECT TOP 10 id, COALESCE(x.boy, x.girl, x.dog, x.cat) as Who
    FROM house x

Answer 3

试试这个：

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

虽然您可以像Joe建议的那样使用coalesce。

tsql：是否可以在select中执行嵌套的case语句？

3 个答案: