SQL: 将 CASE 与 AS 结合使用

Question

我正在处理一个很长的 SQL 请求，我想在里面使用 CASE，但我不知道如何写。我的请求看起来像：

SELECT (
    SELECT id FROM first_table ft 
    INNER JOIN second_table st ON st.id = ft.id
    INNER JOIN third_table tt ON tt.id = ft.id WHERE tt.second = 0 LIMIT 1
) as key

我想添加如下内容：

CASE key WHEN 'One' THEN 'Two' END

我试着在最后添加这个，但没有成功:

SELECT (
    SELECT id FROM first_table ft
    INNER JOIN second_table st
        ON st.id = ft.id
    INNER JOIN third_table tt
        ON tt.id = ft.id WHERE tt.second = 0 LIMIT 1
) as key CASE WHEN key = 'One' THEN 'Two' END

我的目标是根据值编辑键

Answer 1

你可以做一个子查询：

SELECT
   key,
   CASE WHEN key = 'One' THEN 'Two' END test_column
FROM
   (
      SELECT 
         id key
      FROM
         first_table ft
         INNER JOIN second_table st ON st.id = ft.id
         INNER JOIN third_table tt ON tt.id = ft.id
      WHERE 
         tt.second = 0
      LIMIT 1
   ) data

SQL: 将 CASE 与 AS 结合使用

SQL: use CASE with AS

sql

case