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 A1, A2, …, An are attributes, T1, T2, …, Tm are tables and C is a Boolean condition expression

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In this example, why is query optimization needed particularly when the tables involved in the query contain a large number of rows?


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