Query Evaluation (cont)
A query in SQL:
- states what answers are required (declarative)
- does not say how they should be computed (procedural)
A query evaluator/processor :
- takes declarative description of query
(in SQL)
- parses query to internal representation
(relational algebra)
- determines plan for answering query
(expressed as DBMS ops)
- executes method via DBMS engine
(to produce result tuples)
Some DBMSs can save query plans for later re-use.
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