Question

我有以下postgresql选择

       SELECT 
            col1,
            col2,
            col3,
       CASE
           WHEN var = 1
            col4,
            col5,
            col6
           WHEN var = 2
            col7,
            col8,
            col9
           WHEN var =3
            col10,
            col11,
            col12
        END 
FROM A JOIN B .....

所以我只想在 CASE WHEN 条件下选择不同的列但是由于case只返回一个值，这个语句会返回一个错误，有没有办法使这个工作？

Answer 1

您需要多个CASE表达式：

SELECT col1, col2, col3,
       (CASE WHEN var = 1 THEN col4
             WHEN var = 2 THEN col7
             WHEN var = 3 THEN col10
        END),
       (CASE WHEN var = 1 THEN col5
             WHEN var = 2 THEN col8
             WHEN var = 3 THEN col11
        END),
       (CASE WHEN var = 1 THEN col6
             WHEN var = 2 THEN col9
             WHEN var = 3 THEN col12
        END)
FROM A JOIN B .....

在案例中选择多个列

1 个答案: