liyafan82 opened a new pull request #2355:
URL: https://github.com/apache/calcite/pull/2355
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 (`NDV({1})` denotes the number of distinct values for column 1), 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.
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
