What generic techniques can be applied to optimize SQL queries?

Question

What techniques can be applied effectively to improve the performance of SQL queries? Are there any general rules that apply?

Answer 1

• Use primary keys
• Avoid select *
• Be as specific as you can when building your conditional statements
• De-normalisation can often be more efficient
• Table variables and temporary tables (where available) will often be better than using a large source table
• Partitioned views
• Employ indices and constraints