[CALCITE-695] Do not add SINGLE_VALUE aggregate function to a sub-query that will never return more than one row

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.3.0-incubating
• Fix Version/s: 1.3.0-incubating
• Assignee: Julian Hyde
• Reporter: Aman Sinha
• Created: 23/Apr/15 19:10
• Updated: 01/Jun/15 18:24
• Resolved: 02/May/15 01:46

Description

In the following query, the subquery is producing a scalar value but the logical plan still creates a SqlSingleValueAggFunction.

select r_regionkey from region
   where r_regionkey > (select min(n_regionkey) * 2 from nation);

If the aggregate is just min(n_regionkey) instead of the expression min(n_regionkey) * 2 then no SqlSingleValueAggFunction is created. Ideally, both should behave the same.

This is not necessarily a bug but it does create a burden on the underlying execution engine to support this function even in cases where it may not be needed.