简化嵌套的case when语句 [英] Simplify nested case when statement

问题描述

下面是我当前的SELECT CASE语句：

Below is my current SELECT CASE statement:

SELECT CASE 
WHEN edition = 'STAN' AND has9 = 1 THEN '9'
WHEN edition = 'STAN' AND has8 = 1 THEN '8'
WHEN edition = 'STAN' AND has7 = 1 THEN '7' 
WHEN edition = 'STAN' AND hasOLD = 1 THEN 'OLD'
WHEN edition = 'SUI'  AND has_s9 = 1 THEN 'S9' 
WHEN edition = 'SUI'  AND has_s8 = 1 THEN 'S8' ELSE 'S7' END AS version

我并不总是希望重复版本='xxx'的条件，例如

I do not always want to repeat the edition = 'xxx' condition, such as

CASE WHEN edition = 'STAN' AND has9 = 1 THEN '9' ELSE WHEN has8 = 1 THEN '8' ELSE WHEN has7 = '7' ELSE WHEN edition 'SUI' AND has_s9 = 1 THEN 'S9' ELSE ...

在Excel中，这相当容易，但是如何在PostgreSQL中编译呢？

In Excel this is fairly easy but how can I compile that in PostgreSQL?

推荐答案

尝试一下

SELECT CASE 
WHEN edition = 'STAN' THEN 
     CASE 
          WHEN has9 = 1 THEN '9'
          WHEN has8 = 1 THEN '8'
          WHEN has7 = 1 THEN '7'
          WHEN hasOLD = 1 THEN 'OLD'
     END
WHEN edition = 'SUI' THEN
     CASE 
          WHEN has9 = 1 THEN 'S9'
          WHEN has8 = 1 THEN 'S8'
     END
ELSE 'S7' END AS version

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