Query Processor

It is responsible for parsing, translating, optimizing and evaluating queries.

There are 2 alternative ways to evaluate a query:

• using equivalent expressions

• using different algorithms for each operation

We must choose the method that has the least cost.

There are two approaches to select the best query evaluation plan:

• cost-based: considers the cost of the operations; however, it needs statistical information about data in the database

• rule-based: uses a set of rules to determine how to execute a query