MYSQL CASE THEN statement with multiple values

Question

I am trying go select multiple values with CASE statement. I noticed we cannot do

CASE 
    WHEN wall.type=\"bk\" 
    THEN books.id1,books.id2, //         


        

Answer 1

No, it is just a single value. Additionally, it is contradictory to use "multiple columns" and name those multiple columns as column_1, right? :)

You can use another column to store the other id with (a similar case) and use nulls to represent the else values, just like you're doing now.

Example:

CASE 
    WHEN wall.type="bk" 
    THEN books.id1
END as column_1,
CASE 
    WHEN wall.type="bk" 
    THEN books.id2
END as column_2

Check the official documentation for more information.