Github user Tagar commented on the issue:
https://github.com/apache/spark/pull/16228
@wzhfy, thanks for the feedback.
For outer joins, cardinaility estimates should be:
- left_outer_join_cardinality(table_A, table_B) = MAX(cardinality(A),
inner_join_cardinality(table_A, table_B))
So with left outer join, you'll get join cardinality at least number of
the rows on the left (table A);
- right outer join is similar to left outer join (with exception s/A/B/g);
- full_outer_join_cardinality(table_A, table_B) = cardinality(A) +
cardinality(B) - inner_join_cardinality(table_A, table_B)).
Does this sound about right?
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