高级SQL查询或谜题的好书或网站？

I work with SQL almost on a daily basis and want to improve my SQL skills. I am looking for online resources or books for advanced queries for real life problems. I liked Joe Celko's books and I am looking for similar resources. I am also interested in SQL puzzles but ones which solve real life business apps. I am not into brain teasers, chess, games, cards and the like of SQL problems which look overly complicated or too obscure to be useful.I work with SQL almost on a daily basis and wan