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https://issues.apache.org/jira/browse/CALCITE-7199?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ruben Q L updated CALCITE-7199:
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Summary: Improve column uniqueness computation for Join (was:
RelMdColumnUniqueness joins handler is invalid for columns in both sides)
> Improve column uniqueness computation for Join
> ----------------------------------------------
>
> Key: CALCITE-7199
> URL: https://issues.apache.org/jira/browse/CALCITE-7199
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.40.0
> Reporter: Claude Brisson
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.41.0
>
>
> {{RelMdColumnUniqueness.areColumnsUnique()}} handler for joins contains the
> following code:
> {code}
> // If the original column mask contains columns from both the left and
> // right hand side, then the columns are unique if and only if they're
> // unique for their respective join inputs
> Boolean leftUnique = mq.areColumnsUnique(left, leftColumns, ignoreNulls);
> Boolean rightUnique = mq.areColumnsUnique(right, rightColumns,
> ignoreNulls);
> if ((leftColumns.cardinality() > 0)
> && (rightColumns.cardinality() > 0)) {
> if ((leftUnique == null) || (rightUnique == null)) {
> return null;
> } else {
> return leftUnique && rightUnique;
> }
> }
> {code}
> This is not correct. Uniqueness on both sides is a sufficient condition for
> the columns to be unique in the join result, but not a necessary one.
> The columns will also be unique in the joins result if the following
> conditions are all met:
> * the queried columns coming from the left input are unique
> * the columns implied in the right side of the join equi-condition are unique
> * the join does not generate nulls on the left
> (and the same with left and right reversed).
> The fact that the join is done on a unique key on the right side will
> guarantee that the uniqueness of the queried columns on the left is
> preserved, and whatever columns we add in the queried subset, it will remain
> unique.
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