Use the example schema (16.4) on page 703 to design a query for finding the names of all managers (employees with Title = ’manager’) whose salary is more than |S20,000, but assume that there are three warehouses. Also assume that the total number of employees is 100,000, that 5000 of them make over |S20,000, that the total number of managers is 50, and that 90% of the managers make more than |S20,000.
What will be an ideal response?
The best alternative is the one given in the text.
1. At each of the warehouse sites, select all tuples for which the title is manager.
2. Send these tables to the headquarters site. Do the join there, Then send the sames to site A
The number of bytes to be sent is exactly the same as in the text — 1,300 bytes from
all the warehouse sites to the headquarters, plus 675 bytes from the headquarters site
to site A, for a total of 1,975 bytes.
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