Query Optimization Example Source: Query Optimization, Y. E. Ioannidis, ACM Computing Surveys, 28(1), March Database Tables: Emp (name, age, sal, dno) Dept (dno, dname, floor, budget, mgr, ano) Acnt (ano,t ype, balance, bno) Bank (bno, bname,a ddress) Query Q: select name, floor from emp, dept where emp.dno=dept.dno and sal>100K. System Catalog Information: Table Emp: 20,000 pages, 100,000 tuples, clustering B+tree index on emp.sal (3-levels) selectivity( salary > 100K) = 10 percent Table Dept: 10 pages, 100 tuples, clustering Hash-file on dept.dno (1.2 pages/bucket) Memory Buffer: 3 pages Disk I/O cost: 20 ms/page

Algebraic Tree Transformations

Dynamic Programming: Step 1 – Options at Leafs

Step 2a – Options for Join – nested loop

Step 2 – Options for Join

Semantic Query Optimization Query Q: select name, floor from emp, dept where emp.dno=dept.dno And job = “Sr. Programmer” Integrity Constraint: assert sal-constraint on emp: sal>100K where job = “Sr. Programmer” Query Q’: select name, floor from emp, dept where emp.dno=dept.dno and job = “Sr. Programmer” and sal>100K. System Catalog Information: Table Emp: 20,000 pages, 100,000 tuples, clustering B+tree index on emp.sal (3-levels) selectivity( salary > 100K) = 10 percent Table Dept: 10 pages, 100 tuples, clustering Hash-file on dept.dno (1.2 pages/bucket) Memory Buffer: 3 pages Disk I/O cost: 20 ms/page Q? Compare queries Q and Q’ on Query Result Efficiency of query plans