Compare the cost of two different query plans for the following query: Salary < 40000 (EMPLOYEE
Question:
Compare the cost of two different query plans for the following query:
σSalary< 40000(EMPLOYEE ∞ Dno=DnumberDEPARTMENT)
Use the database statistics shown in Figure 19.6.
Figure 19.6
Transcribed Image Text:
Figure 19.6 Sample statistical information for relations in Q2. (a) Column information. (b) Table information. (c) Index information. (a) Table_name Column_name Num_distinct Low_value High_value PROJECT Plocation 200 200 PROJECT Pnumber 2000 1 2000 PROJECT Dnum 50 1 50 DEPARTMENT Dnumber DEPARTMENT Mgr_ssn 50 1 50 50 1 50 ΕMPLOYEΕ Ssn 10000 1 10000 ΕMPLOYEΕ Dno 50 1 50 EMPLOYEE Salary 500 1 500 (b) Table_name Num_rows Blocks PROJECT 2000 100 DEPARTMENT 50 EMPLOYEE 10000 2000 (c) Index_name Uniqueness Blevel* Leaf_blocks Distinct_keys PROJ_PLOC NONUNIQUE 1 200 EMP_SSN UNIQUE 1 50 10000 EMP SAL NONUNIQUE 1 50 500 *Blevel is the number of levels without the leaf level.
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Related Book For
Fundamentals Of Database Systems
ISBN: 9780133970777
7th Edition
Authors: Ramez Elmasri, Shamkant Navathe
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