Professional test of skills using real life SQL problem, they called me in for a 2-day skills test. The key was showing a general understanding of the data structures they presented as well as showing genuine interest in the company. Do all of the beginning steps if you aren't sure of the solution right away, e.g. data flows and a context diagram. Make sure your test computer is setup for running large queries, when I got there the computer they gave me only had a few MB's left of space, so the first big queries I ran chugged it to a grinding halt with no saved work.