Notes06

# Notes06 - CS245:DatabaseSystem Principles...

This preview shows pages 1–16. Sign up to view the full content.

CS 245 Notes 6 1 CS 245: Database System  Principles Notes 6: Query Processing Steven Whang

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 2 Query Processing Q      Query Plan Focus:  Relational System Others?
CS 245 Notes 6 3 Example Select B,D From R,S Where R.A = “c”     S.E = 2     R.C=S.C

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 4 R A B C S C D E a 1 10 10 x 2 b 1 20 20 y 2 c 2 10 30 z 2 d 2 35 40 x 1 e 3 45 50 y 3 Answer B D 2 x
CS 245 Notes 6 5  How do we execute query? - Do Cartesian product - Select tuples - Do projection One idea

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 6 RXS R.A R.B R.C S.C S.D S.E a 1 10 10 x 2 a 1 10 20 y 2 . . C 2 10 10 x 2 . . Bingo! Got one. ..
CS 245 Notes 6 7 Relational Algebra  - can be used to    describe plans. .. Ex:  Plan I Π B,D   σ R.A =“c”  S.E=2   R.C=S.C X R S OR:    Π B,D  [   σ R.A=“c”  S.E=2   R.C = S.C  (RXS)]

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 8 Another idea: Π B,D    σ R.A = “c”   σ S.E = 2 R   S Plan II natural join
CS 245 Notes 6 9    R         S A  B  C σ ( R ) σ ( S )      C  D  E a  1  10        A   B  C       C  D  E     10  x  2 b  1  20 c   2  10     10  x  2     20  y  2 c  2  10        20  y  2     30  z  2 d  2  35        30  z  2     40  x  1 e  3  45                                         50  y  3

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 10 Plan III  Use R.A and S.C Indexes (1) Use R.A index to select R tuples    with R.A = “c” (2) For each R.C value found, use S.C   index to find matching tuples (3) Eliminate S tuples S.E   2 (4) Join matching R,S tuples, project    B,D attributes and place in result
CS 245 Notes 6 11    R         S A  B  C      C  D  E a  1  10                  10  x  2 b  1  20     20  y  2 c  2  10             30  z  2 d  2  35             40  x  1 e  3  45                                         50  y  3 A C I 1 I 2 =“c” <c,2,10> <10,x,2> check=2? output: <2,x> next tuple: <c,7,15>

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 12 Overview of Query Optimization
CS 245 Notes 6 13 parse convert apply laws estimate result sizes consider physical plans estimate costs pick best execute {P1,P2,…. .} {(P1,C1),(P2,C2). ..} Pi    answer SQL query parse tree logical query plan “improved” l.q.p l.q.p. +sizes statistics

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CS 245 Notes 6 14 Example:    SQL query SELECT title FROM StarsIn WHERE starName IN ( SELECT name FROM MovieStar WHERE birthdate LIKE ‘%1960’ ); (Find the movies with stars born in 1960)
CS 245 Notes 6 15 Example:    Parse Tree <Query> <SFW> SELECT   <SelList>    FROM    <FromList>     WHERE     <Condition>

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This document was uploaded on 03/08/2011.

### Page1 / 84

Notes06 - CS245:DatabaseSystem Principles...

This preview shows document pages 1 - 16. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online