Although this may come as a shock, Microsoft Access is good for this purpose (too bad that it's useless as a database product
). The reason being that, IIRC, you can design queries in the graphical UI, then you can see what SQL it generated for you. In fact, I'll go this far: if you can set up an ODBC link to whatever-database-that-is, you can use the Access frontend to query it.
This goes as general advice too: assuming your queries aren't extremely fancy, the first steps should be with a graphical UI that shows relations between tables and all that jazz, so that he can get the mental model right. Once he's understood some simple queries that way, he can proceed to actually writing SQL.