[CALCITE-4511] The distinct row count and population size for constant columns should be 1

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.27.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Liya Fan
• Reporter: Liya Fan
• Created: 23/Feb/21 04:52
• Updated: 03/Jun/21 22:32
• Resolved: 15/Apr/21 04:20

Description

Suppose we have a relation with 3 columns: (a, '1', '2'). The first column comes from an underlying table, while the other two columns are constants.

For this relation, we should have NDV(1) = 1, since column 1 is a constant, which have only one possible value (suppose the column index starts from 0).

Similarly, we should have NDV(1, 2) = 1, since both columns are constants.

We should also have NDV(0, 1) == NDV(0), because the number of distinct values depends on the non-const column, which is a from the underlying table.

Issue Links

• links to: GitHub Pull Request #2355