Github user aokolnychyi commented on the issue:
https://github.com/apache/spark/pull/18909
@gatorsmile I took a look at both PRs.
I quickly scanned PR #14866 and did not find tests for existence joins.
Also, `SQLConf.CROSS_JOINS_ENABLED = true` is checked only for `left_outer`.
So, the proposed tests slightly improve the coverage.
PR #16762 checks everything from a different prospective than the proposed
rules and has some unique scenarios compared to PR #14866. The main question
that PR #16762 rises is about, for instance, inner joins with inequality
conditions. As far as I understood, the ability to detect such cartesian
products was the motivation to move the check away from the Optimizer. Is it
still planned? Cannot this be also done by modifying the existing rule in the
Optimizer? Currently, it only checks that there are conditions which reference
to both sides. Instead, it can rely on equality predicates, right?
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