Most efficient update

[Mark Rigney]

Fairly new to mysql - what would be the most efficient way to accomplish the following? I have a table w/ roughly 3 million rows and another table with roughly 12 million. The smaller table has a field that is a foreign key into the larger table. What I need to do is update each record in the larger table that has a matching entry in the smaller table.

Originally I was selecting all the records from the smaller table then rolling thru row by row updating the larger table when need be... but this is taking way too long.

Thanks in advance for any help.