A generic SQL statement like the following can be translated directly to a relational algebra expression:
SELECT A1, A2, …, An FROM T1, T2, …, Tm WHERE C
A1, A2, …, An are attributes,
T1, T2, …, Tm are tables and
C is a Boolean condition expression
In this example, why is query optimization needed particularly when the tables involved in the query contain a large number of rows?