These are some tips that need to know before start of database performace start.
1. Database performance can not be learn without learning of database architecture.
2. Index creation is not database performance tuning.
3. 80% of the database performance problem is due to sql query write.
4. Most of time database architecture is not properly designed.
5. Most organization think that application developer can build database and its programming.
6. Most of time database capacity and performance planing is not done.
7. Each and every single query need to be performance tested before moving to production.
8. Before creating index we have to check side effect of that index on database.
9. Full table scan is not a problem every time.
10. At some extent business logic should be clear before selecting data from database. This will reduce amount of data.