Database indices increase performance

Note to self: Remember to add indices on those columns that will be used in queries as keys.

Links to index related documentation in each of the popular databases:

• MySQL 5.5: How MySQL Uses Indexes
• PostgreSQL 9.1: Index Types
• MongoDB: Indexes
• SQLite 3: The SQLite Query Planner

Like all of the documentation linked above states that index is something that can easily increase performance if designed properly.

Therefore, do only proper assigning of indices.