Update values from one column in same table to another in SQL Server

Question

I\'m trying to overwrite values that are found in TYPE1 with values that are found in TYPE2.

I wrote this SQL to try it out, but for some reason it isn\'t updating:<

Answer 1

update TABLE_1 a set COLUMN_1 = (select COLUMN_2 from TABLE_1 b where a.ID = b.ID)