我如何使用 T-SQL 的 Case/When? [英] How do I use T-SQL's Case/When?

问题描述

我有一个很大的查询，它经常使用case/when.现在我这里有这个 SQL，它不起作用.

I have a huge query which uses case/when often. Now I have this SQL here, which does not work.

 (select case when xyz.something = 1
 then
     'SOMETEXT'
 else
      (select case when xyz.somethingelse = 1)
      then
          'SOMEOTHERTEXT'
      end) 

      (select case when xyz.somethingelseagain = 2)
      then
          'SOMEOTHERTEXTGOESHERE'
      end)
 end) [ColumnName],

引起问题的是xyz.somethingelseaagain = 2，它说它无法绑定该表达式.xyz 是在查询中进一步连接的表的别名.这里有什么问题?删除 2 个 case/whens 中的一个可以纠正这一点，但我需要它们两个，甚至可能更多的情况.

Whats causing trouble is xyz.somethingelseagain = 2, it says it could not bind that expression. xyz is some alias for a table which is joined further down in the query. Whats wrong here? Removing one of the 2 case/whens corrects that, but I need both of them, probably even more cases.

推荐答案

SELECT
   CASE 
   WHEN xyz.something = 1 THEN 'SOMETEXT'
   WHEN xyz.somethingelse = 1 THEN 'SOMEOTHERTEXT'
   WHEN xyz.somethingelseagain = 2 THEN 'SOMEOTHERTEXTGOESHERE'
   ELSE 'SOMETHING UNKNOWN'
   END AS ColumnName;

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