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Queries, behind the scene
Imperative query execution plan:
SELECT C.name
FROM
Students S, Takes T, Courses C
WHERE
S.name=“Mary” and
S.ssn = T.ssn and T.cid = C.cid
Declarative SQL query
Students
Takes
sid=sid
sname
name=“Mary”
cid=cid
Courses
The optimizer
chooses the best execution plan for a query