SQL update statement

In simplistic terms here is what I want to do: update file_a set file_a.a2 = "C" where file_a.a1 = file_b.a1 I know that I have to do a correlated subquery but I can't figure out the right syntax. I thought that the example on page 131 of Jonathan Leffler's book would yield the answer but I haven't been able to convert his example to my specific case. His example is: update models set price = price + 100 + 0.03 * (select max(hi_price) from prices where prices.model = models.model and exists (select * from prices where prices.model = models.model) ); I hope this is enough information. Thanks ~