MySql在有值时选择多个列

Question

我需要从表中选择一些列，还需要根据一列中的值选择其他列。例如：

 SELECT 
    col_a, col_b, col_c
FROM user_table 

INNER JOIN col_d, col_e, col_f ON col_type = 1
INNER JOIN col_g, col_h, col_i ON col_type = 2

WHERE id = :id
AND active = 1

由于我是mysql的新手，我不知道应该如何做到这一点。我尝试使用CASE WHEN，但能够选择一个列，我需要选择多个列。

Answer 1

我认为你误解了INNER JOIN，你想要那样的东西

SELECT 
    col_a, col_b, col_c,
    IF( col_type = 1, col_d, NULL ) AS col_d,
    IF( col_type = 1, col_e, NULL ) AS col_e,
    IF( col_type = 2, col_g, NULL ) AS col_g,
    IF( col_type = 2, col_h, NULL ) AS col_h
FROM user_table 

WHERE id = :id
AND active = 1

但我更喜欢加载所有cols并用你的其他语言处理它（PHP？）。