Julian Hyde created CALCITE-4687: ------------------------------------ Summary: Add LIMIT to WITHIN GROUP clause of aggregate functions Key: CALCITE-4687 URL: https://issues.apache.org/jira/browse/CALCITE-4687 Project: Calcite Issue Type: Bug Reporter: Julian Hyde
Add LIMIT to WITHIN GROUP clause of aggregate functions. LIMIT is not in the SQL standard, but it is useful, and is not hard to implement. The following query computes the 3 highest paid employees in each department: {code:java} SELECT deptno, ARRAY_AGG(sal) WITHIN GROUP (ORDER BY sal DESC LIMIT 3) FROM Emp GROUP BY deptno {code} It can be implemented efficiently (using a merge sort that discards all but the top 3 rows in each key, at each pass). Note that BigQuery does not support the {{WITHIN GROUP}} clause, but in the {{ARRAY_AGG}} function, the {{ORDER BY}} and {{LIMIT}} sub-clauses appear within the parentheses, like this: {{ARRAY_AGG(sal ORDER BY sal DESC LIMIT 3)}}. In Calcite, you can use either syntax for {{ARRAY_AGG}}, {{ARRAY_CONCAT_AGG}}, {{GROUP_CONCAT}}, {{STRING_AGG}} functions; we should add {{LIMIT}} in both. -- This message was sent by Atlassian Jira (v8.3.4#803005)