Query Processing :-
Query Processing would mean the entire process or activity which involves query translation into low level instructions, query optimization to save resources, cost estimation or evaluation of query, and extraction of data from the database.
Goal: To find an efficient Query Execution Plan for a given SQL query which would minimize the cost considerably, especially time.
Cost Factors: Disk accesses [which typically consumes time], read/write operations [which typically needs resources such as memory/RAM].
The major steps involved in query processing are depicted in the figure below;