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SELECT AVG(salary)
FROM salesperson
SAMPLE RANDOM 10 PERCENT CLUSTERS OF 4 BLOCKS;
(EXPR)
---------------------
--- 1 row(s) selected.
For this query execution, the number of rows returned is limited by the total number of
rows in the SALESPERSON table. Therefore, it is possible that no rows are returned, and
the result is null.
•
This query illustrates sampling after execution of the WHERE clause has chosen the qualifying
rows. The query computes the average salary of a random 10 percent of the sales people
over 35 years of age. You will get a different result each time you run this query because it
is based on a random sample.
SELECT AVG(salary)
FROM salesperson
WHERE age > 35
SAMPLE RANDOM 10 PERCENT;
(EXPR)
--------------------
--- 1 row(s) selected.
•
Compute the average salary of a random 10 percent of sales people belonging to the
CORPORATE department. The sample is taken from the join of the SALESPERSON and
DEPARTMENT tables. You will get a different result each time you run this query because
it is based on a random sample.
SELECT AVG(salary)
FROM salesperson S, department D
WHERE S.DNUM = D.DNUM
AND D.NAME = 'CORPORATE'
SAMPLE RANDOM 10 PERCENT;
(EXPR)
---------------------
--- 1 row(s) selected.
•
In this example, the SALESPERSON table is first sampled and then joined with the
DEPARTMENT table. This query computes the average salary of all the sales people
belonging to the CORPORATE department in a random sample of 10 percent of the sales
employees.
SELECT AVG(salary)
FROM ( SELECT salary, dnum
WHERE S.DNUM = D.DNUM
AND D.NAME = 'CORPORATE';
(EXPR)
--------------------
264
SQL Clauses
50219.524
58000.00
106250.000
FROM salesperson
SAMPLE RANDOM 10 PERCENT ) AS S, department D
37000.000
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