where Emp21 is stored at site B and Emp22 is stored at site C. A query at site A wants the names of all managers in the accounting department whose salary is greater than their age. Design a plan for this query, using the assumptions on page 704 for table and attribute sizes. Assume that the items in the Age column are two bytes long.
Suppose that we have a relation
Employee2 (SSnum, Name, Salary, Age, Title, Location)
which is partitioned as
Emp21 (SSnum, Name, Salary)
Emp22 (SSnum, Title, Age, Location)
What will be an ideal response?
1. At site C performs a SELECT statement that returns the SSnum and Age of all
employees for which Title = ‘Manager’. Call this table T1
2. Send T1 to site B. Since there are 50 managers, the total amount of information that must be sent is 50 ? (9 + 6) or 750 bytes
3. At site B, perform the join of T1 with Emp21, select those names whose salary is greater than their age, and send the result to site A.
Since we do not knowhowmany managers have a salary greater than their age we cannot estimate the communication costs for the third step.
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