1. Don't use UPDATE instead of CASE
This issue is very common, and though it's not hard to spot, many developers often overlook it because using UPDATE has a natural flow that seems logical.

Database performance relies on several layers ranging from operation system, hardware, network, devices, database server, database design, to client side SQL query design in an application. The bottleneck could lay on any layer. However , once the system environments have been established and a database has been properly designed, the performance of the database mainly depends on properly created indexes and SQL query design. Accordiing to Sybase , 80% of Sybase database performance problems can be solved by properly created index and carefully design of SQL queries.