How to use a select statment inside a case statement

Question

I will do a select statement inside my case statement like this:

CASE
    WHEN d.dependent_speed_type = 4 THEN (SELECT column FROM tablename) 
END

But this is not working. Can I realize a select statement inside my case statement? If the value 4 is inside my column "d.dependent_speed_type" then it should be select a special value from another table. How is the right syntax?

Answer 1

您必须使用总是返回一个值的东西，例如SELECT MAX(column) FROM tablename) 。