Yeah CASE was the wrong term to use. Looks like I want something like this:

IF ((SELECT DATEPART(MONTH, GetDate())) = 04)

UPDATE

db1

SET

column1 = db2.value

FROM

db2

However, when using this it copies only the first row from db2 into all rows of db1. I want all rows of db2 into all rows of db1 for column1.