[CALCITE-4241] Some improvements to metadata query

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.26.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Liya Fan
• Reporter: Liya Fan
• Created: 10/Sep/20 07:12
• Updated: 06/Oct/20 17:16
• Resolved: 21/Sep/20 11:53

Description

1. For {{RelMdColumnUniqueness#areColumnsUnique(RelSubset, RelMetadataQuery,
   ImmutableBitSet, boolean)}}, we can return early as we encounter the first null.
2. For {{RelMdDistinctRowCount#getDistinctRowCount(Values, RelMetadataQuery,
   ImmutableBitSet, RexNode)}}, we can get the distinct row count accurately, instead of guessing that half of the elements are distinct. 
3. RelMdUtil#areColumnsDefinitelyUniqueWhenNullsFiltered could be implemented in a more efficient way. 

Issue Links

• links to: GitHub Pull Request #2146