HP Neoview SQL Reference Manual page 265

--- 1 row(s) selected.
Note that the results of this query and some of the results of previous queries might return
null:
SELECT AVG(salary)
FROM ( SELECT salary, dnum
FROM salesperson
SAMPLE RANDOM 10 PERCENT ) AS S, department D
WHERE S.DNUM = D.DNUM
AND D.NAME = 'CORPORATE';
(EXPR)
--------------------
--- 1 row(s) selected.
For this query execution, the number of rows returned by the embedded query is limited
by the total number of rows in the SALESPERSON table. Therefore, it is possible that no
rows satisfy the search condition in the WHERE clause.
• In this example, both the tables are sampled first and then joined. This query computes the
average salary and the average sale amount generated from a random 10 percent of all the
sales people and 20 percent of all the sales transactions.
SELECT AVG(salary), AVG(amount)
FROM ( SELECT salary, empid
FROM salesperson
SAMPLE RANDOM 10 PERCENT ) AS S,
( SELECT amount, empid
FROM sales
SAMPLE RANDOM 20 PERCENT ) AS T
WHERE S.empid = T.empid;
(EXPR) (EXPR)
--------- ---------
45000.00 31000.00
--- 1 row(s) selected.
• This example illustrates oversampling. This query retrieves 150 percent of the sales
transactions where the amount exceeds $1000. The result contains every row at least once,
and 50 percent of the rows, picked randomly, occur twice.
SELECT *
FROM sales
WHERE amount > 1000
SAMPLE RANDOM 150 PERCENT;
EMPID PRODUCT
----- --------------------
1 PCGOLD, 30MB
23 PCDIAMOND, 60MB
23 PCDIAMOND, 60MB
29 GRAPHICPRINTER, M1
32 GRAPHICPRINTER, M2
32 GRAPHICPRINTER, M2
... ...
--- 88 row(s) selected.
?
REGION
------
E
W
W
N
S
S
...
AMOUNT
-----------
30000.00
40000.00
40000.00
11000.00
15000.00
15000.00
...
SAMPLE Clause 265