SQL Query optimization tips for Oracle

When we talk about query optimization, we basically wants to reduce response time for 
SQL Query processing and find more efficient way to process workload. One of the major 
way is make our queries to use indexes so that search time can be reduced. 

We have compiled following basic but helpful tips for making a query to use indexes 
and optimizing a query.

1. Primary Key Search
2. Index on Foreign key
3. Simplified conditions
4. Use Outer Join avoid Not In
5. OR vs UNION
6. Function Based Index
7. Handling NULL Values
8. Index Hints and LIKE