Everyone wants faster database queries, and both SQL developers and DBAs can turn to many time-tested methods to achieve that goal. Unfortunately, no single method is foolproof or ironclad. But even if there is no right answer to tuning every query, there are plenty of proven do's and don'ts to help light the way. While some are RDBMS-specific, most of these tips apply to any relational database.
My previous collection of SQL do's and don'ts concentrated on individual query performance. While you’ll definitely find more of that here, the main focus is on increasing concurrency in your system. By minimizing locking, I/O, and network traffic, you can not only make your queries run much faster, but even more important, you can make queries behave themselves on a system with hundreds or even thousands of concurrent users.