Tuning SQL statements, especially in applications where complex queries are involved, is generally the most efficient means of improving performance.
Be sure to tune your application before tuning the database for the following reasons:
▪ during application design you have control over the SQL statements and data to be processed,
▪ you can improve performance even if you are unfamiliar with the internal working of the database,
▪ if your application is not tuned well, it will not run well even on a well-tuned database.
You should know what data your application processes, what SQL statements are used, and what operations the application performs on the data. For example, you can improve query performance when you keep SELECT statements simple and avoid unnecessary clauses and predicates.