SQL/MX 2.x Reference Manual (G06.24+, H06.03+)

SQL/MX Clauses
HP NonStop SQL/MX Reference Manual—523725-004
7-8
SAMPLE Clause
SAMPLE Clause
Considerations for SAMPLE
Examples of SAMPLE
The SAMPLE clause of the SELECT statement specifies the sampling method used to
select a subset of the intermediate result table of a SELECT statement. The
intermediate result table consists of the rows returned by a WHERE clause or, if there
is no WHERE clause, the FROM clause. See SELECT Statement on page 2-178.
SAMPLE is an SQL/MX extension.
RANDOM percent-size
directs NonStop SQL/MX to choose rows randomly (each row having an unbiased
probability of being chosen) without replacement from the result table. The
sampling size is determined by the percent-size, defined as:
percent-result PERCENT [ROWS
| {CLUSTERS OF number-blocks BLOCKS}]
| BALANCE WHEN condition THEN percent-result PERCENT [ROWS]
[WHEN condition THEN percent-result PERCENT [ROWS]]...
[ELSE percent-result PERCENT [ROWS]] END
specifies the value of the size for RANDOM sampling by using a percent of the
result table. The value percent-result must be a numeric literal.
SAMPLE sampling-method
sampling-method is:
RANDOM percent-size
| FIRST rows-size
[SORT BY colname [ASC[ENDING] | DESC[ENDING]]
[,colname [ASC[ENDING] | DESC[ENDING]]]...]
| PERIODIC rows-size EVERY number-rows ROWS
[SORT BY colname [ASC[ENDING] | DESC[ENDING]]
[,colname [ASC[ENDING] | DESC[ENDING]]]...]
percent-size is:
percent-result PERCENT [ROWS
| {CLUSTERS OF number-blocks BLOCKS}]
| BALANCE WHEN condition
THEN percent-result PERCENT [ROWS]
[WHEN condition THEN percent-result PERCENT [ROWS]]...
[ELSE percent-result PERCENT [ROWS]] END
rows-size is:
number-rows ROWS
| BALANCE WHEN condition THEN number-rows ROWS
[WHEN condition THEN number-rows ROWS]...
[ELSE number-rows ROWS] END