if-then in SQL Server

Question

I need to make a command in SQL Server that should basically say

If table1.columnx = 1
then update table2 set comumnx = 1

It should be very simple but I cannot come up with a solution.

Answer 1

update t2
set columnx = 1
from table1 t1 
inner join table2 t2
on t1.id = t2.id
where t1.columnx = 1