如何在单个 SQL CASE 语句中获取多个列？

Question

我试图从单个 CASE 语句中获取多列（在本例中为 insuredcode、insuredname）。

已尝试以下查询，但它将 insuredcode 和 insuredname 连接为一列。

从这样的 CASE 语句中 return 恰好两列的正确语法是什么？

select
    case
        when a.policyno[2] in ('E', 'W') then c.insuredcode || c.insuredname
        else b.insuredcode || b.insuredname
    end
from prpcmain a
left join prpcinsured_1 b on b.proposalno=a.proposalno 
left join prpcinsured_2 c on c.proposalno=a.proposalno
where a.policyno in (select policyno from policyno_t);

Answer 1

一个CASE语句可以return只能单列不能多列

您需要两个不同的 CASE 语句来执行此操作

select
    case
        when a.policyno[2] in ('E', 'W') then c.insuredcode 
        else b.insuredcode 
    end as insuredcode ,
    case
        when a.policyno[2] in ('E', 'W') then  c.insuredname
        else b.insuredname
    end as insuredname
from prpcmain a
left join prpcinsured_1 b on b.proposalno=a.proposalno 
left join prpcinsured_2 c on c.proposalno=a.proposalno
where a.policyno in (select policyno from policyno_t);

Answer 2

我可以建议一些可能稍微快一些的东西：

SELECT s.insuredcode,s.insuredname FROM (
    SELECT a.policyno,b.insuredcode,b.insuredname
    FROM prpcmain a
    left join prpcinsured_1 b on b.proposalno=a.proposalno 
    WHERE a.policyno[2] not in ('E', 'W')
    UNION ALL
    SELECT a.policyno,c.insuredcode,c.insuredname
    FROM prpcmain a
    left join prpcinsured_2 c on c.proposalno=a.proposalno 
    WHERE a.policyno[2]  in ('E', 'W')
) s
where s.policyno in (select policyno from policyno_t);

关于您的问题，显示了您需要做的事情。

Answer 3

It is simply like if/else condition in any language, you can define your condition in When statement and if it is true, SQL executes the Then statement, otherwise executes Else part, as described below:

     Select 
                 CASE 
                    WHEN (cs.ResultSubmitToHOD = 1) THEN 'HOD'
                    WHEN (cs.ResultSubmitToExamDep = 1) THEN 'Exam'
                    ELSE 'Teacher'
                END AS ResultSubmitStatus
     From dbo.CourseSection as cs

如何在单个 SQL CASE 语句中获取多个列？

How to get multiple columns in a single SQL CASE statement?

sql

informix

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