Identifies the sample to which a row belongs, distinguishing rows belonging to different samples specified in the SAMPLE clause of a SELECT statement.
ANSI Compliance
SAMPLEID is a Teradata extension to the ANSI SQL:2011 standard.
Definition of a Sample ID
The sample ID identifies the sample to which a row belongs in the left-to-right order of the SAMPLE clause specification, from 1 through n (where n is the number of samples requested in the SAMPLE clause).
Rules and Restrictions for SAMPLEID
The rules and restrictions are:
- You can only specify SAMPLEID with a SAMPLE clause, which can appear either as part of a select list or as an ORDER BY clause expression.
- SAMPLEID cannot be the only term specified in the select list. If you specify SAMPLEID, you must also specify at least one other non-SAMPLEID column expression.
Using SAMPLEID with Stratified Sampling
The SAMPLEID value for stratified sampling is simply 1, 2, 3, … n across n specified samples regardless of stratification. That is, for the following SAMPLE clause,
SAMPLE WHEN state = 'CA' THEN 0.3, 0.2 ELSE 0.5, 0.2
the SAMPLEID correspondence is:
| 0.3 | 0.2 | 0.5 | 0.2 |
|---|---|---|---|
| 1 | 2 | 3 | 4 |