Beginner to professional the complexity of SQL is the same. It does need lot of practice and trial and error. So that you will learn more.
List of resources which have SQL puzzles:
- The SQLZOO is also one of the good site.
- Joe Celko blog – A great resource Joe Celko books are of great resource. You will improve your SQL knowledge so quickly (See below).
- SQL Forums SriniForum
- Beyond Rational is one of the best site
- Practical Skills of SQL ( Pre-registration required)
- Simple Talk and Oracle forums
- Reading Books from Joe Celko is one of the best way you can improve your SQL knowledge
- Practice SQL online with tutorials point
- Joe Celko’s Analytics and OLAP in SQL (Morgan-Kaufmann, 2006)
- Joe Celko’s Data and Databases (Morgan Kaufmann, 1999)
- Joe Celko’s SQL for Smarties (4-th Edition, Morgan-Kaufmann, 2010)
- Joe Celko’s SQL Programming Style
- Joe Celko’s SQL Puzzles and Answers (2nd edition, Morgan-Kaufmann 2006)
- Joe Celko’s Trees and Hierarchies in SQL for Smarties, 2nd Edition (Morgan-Kaufmann, 2012)
- Joe Celko’s Thinking in Sets: Auxiliary, Temporal, and Virtual Tables in SQL. (Morgan-Kaufmann, 2008)
- Joe Celko’s Data, Measurements and Standards in SQL