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. CASE statement can only return a single value, so the only way to achieve what you want is duplicate the case ...

The database server should be optimized and perform only one time the check on the same condition ...