SQL/MX 2.x Reference Manual (H06.04+)

SQL/MX Clauses
HP NonStop SQL/MX Reference Manual—540440-003
7-13
Examples of SAMPLE
36000.00
...
--- 17 row(s) selected.
In this example, there are 62 rows in the SALESPERSON table. For each set of 20
rows, the first five rows are selected. The last set consists of two rows, both of
which are selected.
•
Compute the average salary of a random 10 percent of the sales people. 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
SAMPLE RANDOM 10 PERCENT;
(EXPR)
--------------------
61928.57
--- 1 row(s) selected.
•
Compute the average salary of a random 10 percent of the sales people using
cluster sampling where each cluster is 4 blocks. 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
SAMPLE RANDOM 10 PERCENT CLUSTERS OF 4 BLOCKS;
(EXPR)
---------------------
50219.524
--- 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)
--------------------
58000.00