Often you may be faced with a requirement to optimize a SQL query (increase query running time) to be executed in Oracle database. Query Optimization in general is a huge topic to discuss. Let me provide some basic steps to be followed while optimizing a SQL query.
1. If the query has only one table and certain where conditions, then try to index the columns given in the where condition. By default primary key columns are indexed. Then try to reorder the set of where conditions based on number of rows for the column values in descending order.