The query optimizer is the component of a database 
management system to optimize the query. Query optimization 
is a function of many relational database management 
systems in which multiple query plans for satisfying a 
query are examined and a good query plan is identified. 


Oracle supports two different Oracle query optimizers, a 
rule-based optimizer and a cost-based optimizer. With 
Oracle Database 10g, the rule-based optimizer is 
desupported.