I have a table of purchases containing a user_id and a date_of_purchase.

I need to be able to select all the users who have made 2 purchases within 12 months of each other. The dates can be any point in time as long as they are less than 12 months apart.

e.g.

user_id      date_of_purchase
123          01/Jan/2010
124          01/Aug/2010
123          01/Feb/2010
124          05/Aug/2008

In this example i want user_id 123