[jira] [Created] (CALCITE-4484) Add UNIQUE_VALUE(x) aggregate function, that throws if x is not unique

["Julian Hyde (Jira)" <ji...@apache.org>]

Julian Hyde created CALCITE-4484:
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             Summary: Add UNIQUE_VALUE(x) aggregate function, that throws if x is not unique
                 Key: CALCITE-4484
                 URL: https://issues.apache.org/jira/browse/CALCITE-4484
             Project: Calcite
          Issue Type: Bug
            Reporter: Julian Hyde


Add a {{UNIQUE_VALUE\(x)}} aggregate function, that throws if {{x}} is not unique.

{{UNIQUE_VALUE\(x)}} would throw if {{x}} has values [1, 2], or has values [1, NULL]; but would not throw if x has values [1, 1, 1] or [] or [NULL, NULL]. Like {{ANY_VALUE}} it behaves as if {{RESPECT NULLS}} is specified.

There are similar functions:
 * {{ANY_VALUE\(x)}} non-deterministically picks a value. (It is present in BigQuery, MySQL, Snowflake, MSSQL and perhaps others.)
 * {{SINGLE_VALUE\(x)}} returns the value of x if there is just one value (e.g. [1] or [NULL]), NULL if there are no values, throws if there is more than one value (e.g. [NULL, NULL] or [1, 1, 1] or [1, 2]). {{SINGLE_VALUE}} is in Calcite, no other DBs that I am aware of, not documented, but available through SQL. Calcite uses it internally to enforce scalar sub-queries.

BigQuery has an internal function "{{$ANY_AND_CHECK\(x)}}" that is equivalent to {{UNIQUE_VALUE\(x)}}.



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