tsql：是否有可能在select中嵌套case语句？

Question

如何在SQL查询的select子句中嵌入if语句？ 我知道使用大小写的情况下，然后X else y结束，但是如何以同样的方式对记录集中的每条记录执行嵌套。

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 

这里是我的尝试：

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？

Answer 1

您可以用COALESCE简化此。

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

Answer 2

是的。案件中的案件没有任何问题。

虽然，这里是你的脚本，corectly写着：

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 3

尝试了这一点：

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 

虽然你可以只使用​​3210乔建议。