james727 commented on a change in pull request #1618:
URL: https://github.com/apache/arrow-datafusion/pull/1618#discussion_r789947673
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File path: datafusion/src/optimizer/filter_push_down.rs
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@@ -253,33 +176,107 @@ fn split_members<'a>(predicate: &'a Expr, predicates:
&mut Vec<&'a Expr>) {
}
}
+// For a given JOIN logical plan, determine whether each side of the join is
preserved.
+// We say a join side is preserved if the join returns all or a subset of the
rows from
+// the relevant side - i.e. the side of the join cannot provide nulls. Returns
a tuple
+// of booleans - (left_preserved, right_preserved).
+fn lr_is_preserved(plan: &LogicalPlan) -> (bool, bool) {
+ match plan {
+ LogicalPlan::Join(Join { join_type, .. }) => match join_type {
+ JoinType::Inner => (true, true),
+ JoinType::Left => (true, false),
+ JoinType::Right => (false, true),
+ JoinType::Full => (false, false),
Review comment:
I think we have the opposite definition of `preserved` 😠- I've been
using `preserved` to refer to the side that cannot provide nulls - e.g. the
left side of a left join, right side of a right join, both sides of an inner
join.
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