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Copyright © 2004 Pearson Education, Inc.
Chapter 15
Algorithms for Query
Processing and
Optimization
Copyright © 2004 Pearson Education, Inc.
FIGURE 15.1
Typical steps when
processing a highlevel query.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-3
FIGURE 15.2
Outline of the sort-merge algorithm for external sorting.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-4
FIGURE 15.3
Implementation JOIN, PROJECT, UNION,
INTERSECTION, and SET DIFFERENCE by using sortmerge, where R has n tuples and S has m tuples. (a)
Implementing the operation T  R <project> A=BS.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-5
FIGURE 15.3 (continued)
Implementation JOIN, PROJECT, UNION,
INTERSECTION, and SET DIFFERENCE by using sortmerge, where R has n tuples and S has m tuples. (b)
Implementing the operation T  <attribute list>(R).
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-6
FIGURE 15.3 (continued)
Implementation JOIN, PROJECT, UNION,
INTERSECTION, and SET DIFFERENCE by using sortmerge, where R has n tuples and S has m tuples. (c)
Implementing the operation T  R  S.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-7
FIGURE 15.3 (continued)
Implementation JOIN, PROJECT, UNION,
INTERSECTION, and SET DIFFERENCE by using sortmerge, where R has n tuples and S has m tuples. (d)
Implementing the operation T  R  S.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-8
FIGURE 15.3 (continued)
Implementation JOIN, PROJECT, UNION,
INTERSECTION, and SET DIFFERENCE by using sortmerge, where R has n tuples and S has m tuples. (e)
Implementing the operation T  R – S.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-9
FIGURE 15.4
Two query trees for the query Q2. (a) Query tree
corresponding to the relational algebra expression for
Q2.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-10
FIGURE 15.4 (continued)
Two query trees for the query Q2. (b) Initial (canonical)
query tree for SQL query Q2.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-11
FIGURE 15.4 (continued)
Two query trees for the query Q2. (c) Query graph for
Q2.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-12
FIGURE 15.5
Steps in converting a query tree during heuristic
optimization. (a) Initial (canonical) query tree for SQL
query Q.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-13
FIGURE 15.5
(continued)
Steps in converting a
query tree during
heuristic optimization.
(b) Moving SELECT
operations down the
query tree.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-14
FIGURE 15.5
(continued)
Steps in converting a
query tree during
heuristic optimization.
(c) Applying the more
restrictive SELECT
operation first.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-15
FIGURE 15.5 (continued)
Steps in converting a query tree during heuristic
optimization. (d) Replacing CARTESIAN PRODUCT
and SELECT with JOIN operations.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-16
FIGURE 15.5
(continued)
Steps in converting a
query tree during
heuristic optimization.
(e) Moving PROJECT
opeations down the
query tree.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-17
FIGURE 15.6
A query tree for query Q1.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-18
FIGURE 15.7
Two left-deep (join) query trees.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-19
FIGURE 15.8
Sample statistical information for relations in Q2.
(a) Column information. (b) Table information. (c) Index
information.
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 15-20