42 Example Join-- File Information 4 Emp( Fn Char(10), Minit Char, LN Char(20), SSN number(9), Bdate...
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1 Example Join-- File Information Emp(Fn Char(10), • Minit Char, • LN Char(20), • SSN number(9), • Bdate Date, • Addr char(40), • Sex Char, • Salary Number(9,2) , • Dno number(3))
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Transcript of 42 Example Join-- File Information 4 Emp( Fn Char(10), Minit Char, LN Char(20), SSN number(9), Bdate...
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Example Join-- File Information
Emp(Fn Char(10), • Minit Char,
• LN Char(20),
• SSN number(9),
• Bdate Date,
• Addr char(40),
• Sex Char,
• Salary Number(9,2) ,
• Dno number(3))
Employee Numbers
– r = 10,000 records– |r| = 99 bytes/record– Block Size = 512 bytes/block– bf = 5 records/block– b = 2,000 blocks– B+-Tree on Dno:
• Ldno = 3, ddno = 125, sdno= 80, mdno = 47
• BLdno = 434
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Example Join-- File Information
Dept(D# Number(3), • Dname Char(20),
• MGRSSN Number(9),
• MgrStartDate Date)
Dept Numbers
– r = 125 records– |r| = 38 bytes/record– bf = 13 records/block– b = 10 blocks– B+-Tree on D#:
• Ldno = 2, ddno = 125, sdno= 1, mdno = 47
• BLdno = 5
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The Sample Query:
I want to use Emp Dept. What are my
options? Dno=D#
Nested Loop approach. Use B-Tree on Emp.Dno. Use B-Tree on Dept.D# Cluster Employee and Department together.
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Join Query -- Nested Loop
Emp Dept. Dno=D#
CJ1 = bdept + bEmp * bDept
= 10 + 2000 * 10 = 20,010
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Join Query -- B-Tree on D#
Emp Dept. Dno=D#
CJ2D# = bEmp + rEmp * (LDept.D# + 1)
= 2000 + 10000 * (2 + 1)
= 32,000
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Join Query -- B-Tree on Dno
Emp Dept. Dno=D#
CBnDno = L+ (s / (m/2 -1) + s
= 3 + ( / (47/2 -1) + 80
= 3 + 4 1 + 80 = 86 CJ2D# = bDept + rDept * (CBnDno)
= 10 + 125 * (86)
= 10,760
Join Query – B-Tree on Dno Disucssion
This is the better choice.
Note: I have ignored the WTDC here because it would be the same in all cases.
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Join Query -- Clustered Files
Emp Dept. Dno=D#
CJ3 = bR + bs
= 2000 + 10
= 2,010
This is the best choice. Note: it does restrict how the files are stored.
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Join Query – Sort Files First
Emp Dept. Dno=D#
Sort Emp: bR*Log2(bR) = 2,000*11= 22000
Sort Dept: bS*Log2(bS) = 10*4 = 40
CJ3 = bR + bS = 2000+10 = 2010
= = 24050
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Join Query – Build Hash On Emp.DNO
Emp Dept. Dno=D#
Build Hash: bR + rR = 2000+10000 = 12000
Hash Join: = 1+ s = 81 CJ3 = bs + rS*(81) = 10+125*(81) = 10135
= = 22135
Example WTDC
If all columns are needed, we have– |r| = 99+38 -3 (D# stored only once) = 134
– r = rEmp = 10,000
– Bf = floor(512/134) = 3– b = ceil(10,000/3) = 3334– Thus the WTDC = 3334
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