Query Optimizer is a most important component of ( Database Management System ) that is used for analyzes Structured Query Language queries and determines efficient execution mechanisms. By using Query Optimizer we can generates one or more query plans for each query and each have mechanism used to run a query. The most efficient query plan is selected and used to run the query. Database users do not typically interact with a query optimizer, which works in the background. Query Optimizer work on the different query plans for the same query, depending on environmental circumstances. The user runs the query when the server is heavily tasked with multiple simultaneous connections so that in that scenario the Query Optimizer may decide to use a query plan that calls on the created table indexes to satisfy the query, based on limited resources.