isidentical opened a new pull request, #3848:
URL: https://github.com/apache/arrow-datafusion/pull/3848
# Which issue does this PR close?
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Closes #3802 .
# Rationale for this change
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When we know for a fact that an inner join is disjoint, we can estimate the
cardinality of an inner join with (at least) one disjoint column as `0`. From
there, we can derive the cardinality of a left/right and full outer joins.
# What changes are included in this PR?
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We now take an `is_exact` flag in `estimate_join_cardinality` which is only
`true` when both left and right are originating directly from table providers
(which might change in the future if we collect more statistics during
materialization points both in DF and Ballista, and somehow adaptively optimize
the parent plans according to that). If that `is_exact` flag is true and if we
identify a disjoint column when calculating the inner join cardinality, we now
infer the cardinality of an inner join as 0.
Since the cardinality of left/right/full outer joins can be derived from the
inner join's cardinality (e.g. a disjoint left outer join would result with the
number of rows from the left side), this PR also adds support for inferring
their cardinality.
# Are there any user-facing changes?
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No.
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