SAMPLING hint

The SAMPLING hint extracts data at a specified rate. SamplingRate is a floating-point value; 1 means 100% of the data.

Syntax

SELECT /*+ SAMPLING(SamplingRate) */ col1, col2, ...
  FROM table_name
 WHERE ...;

Multiply SamplingRate by 100 to express it as a percentage.

Examples

-- Sample 1% from a range capped at 100,000 matching rows
SELECT /*+ SAMPLING(0.01) */ t_name, time, value
  FROM tag
 WHERE t_name = 'TAG_99'
 LIMIT 100000;

Notes

• SamplingRate is a sampling fraction, not a time interval or result row count.
• Row counts may vary per execution; an exact count corresponding to the rate is not guaranteed.
• Small datasets or low rates may return zero rows.
• With LIMIT as above, sampling applies within the row range capped by LIMIT. For example, SAMPLING(0.5) with LIMIT 1000 samples about 50% of up to 1,000 rows when enough matching data exists. It does not fill the sampled result to 1,000 rows.

Related Documentation

• SELECT Hint Syntax — Complete hint list
• ROLLUP Syntax — Exact time-unit aggregation