Investigate the logical relationship between the SQL operator EXISTS and the TRC quanti?er ?. For concreteness, express query (5.26), page 160, using TRC.
What will be an ideal response?
The SQL EXISTS operator is more limited: it tests whether a set is empty. The ? quanti?er in TRC is more versatile, especially when the query contains universal quanti?ers and the NOT operator in addition to ?. For instance, the query (5.26), can be expressed much more naturally in TRC using ? than in SQL using EXISTS:
{S.Id | Student(S) AND
NOT (?T ? Transcript ?C ? Course
(S.Id = T.StudId AND T.CrsCode = C.CrsCode
AND C.DeptId = ’CS’) )
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