7queryevaluation -suppl_v01.pdf - Query Evaluation...

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Query Evaluation Supplemental slides.
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Execution Plan Skater Selection ࠵? ( age < 10) Participates Join R1.sid = P.sid R1 Project ࠵? (cid, rating) R2 Grouping on cid R3 Selection avg(rating) > 5 Index Nested Loop Sort Scan R4 Count and average R5 Scan Scan Scan SELECT P.cid, count(*), AVG(S.rating) FROM Skaters S, Participates P WHERE P.sid = S.sid AND S.age < 10 GROUP BY P.cid HAVING AVG(S.rating) > 5
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Example Relations Skaters sid cid rank 31 101 2 58 103 7 58 101 7 58 104 1 28 104 2 31 101 3 50 104 3 52 101 4 53 104 4 53 103 5 52 101 6 sid sname rating age 28 Guppy 9 15 31 Debby 7 9 22 Conny 5 9 58 Lilly 10 8 45 Joe 8 7 50 Billy 5 7 52 Beth 6 6 53 Sally 4 7 Participates
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Selection ࠵? ( age < 10) Scan sid sname rating age 31 Debby 7 9 22 Conny 5 9 58 Lilly 10 8 45 Joe 8 7 50 Billy 5 7 52 Beth 6 6 53 Sally 4 7 R1 Output is Pipelined (i.e., each qualified input record is send to output immediately)
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Join R1.sid = P.sid Index Nested Loop sid sname rating age sid cid rank 31 Debby 7 9 31 101 2 58 Lilly 10 8 58 103 7 58 Lilly 10 8 58 101 7 58 Lilly 10 8 58 104 1 31 Debby 7 9 31 101 3 50 Billy 5 7 50 104 3 52 Beth 6 6 52 101 4 53 Sally 4 7 53 104 4 53 Sally 4 7 53 103 5 52 Beth 6 6 52 101 6 R2 Output can be Pipelined (i.e., each qualified input record can be send to output immediately)
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Project ࠵? (cid, rating) Scan Output is Pipelined (i.e., each qualified input record is send to output immediately) rating cid 7 101 10 103 10 101 10 104 7 101 5 104 6 101 4 104 4 103 6 101 R3
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Grouping on cid Sort Last step of sorting can be pipelined in some cases (more in future lectures) But this usually means That this operation does not output Records immediately.
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