SQL

UPDATE with JOIN

To do an update based on a join::

UPDATE tableOne t1 INNER JOIN tableTwo t2 ON t1.fk_two = t2.id SET t1.has_two = 1 WHERE t2.is_good = 1;

JOINs

Useful visual summary: http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins