UBarney commented on code in PR #16210:
URL: https://github.com/apache/datafusion/pull/16210#discussion_r2144201354
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datafusion/physical-plan/src/joins/nested_loop_join.rs:
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@@ -178,6 +187,18 @@ pub struct NestedLoopJoinExec {
metrics: ExecutionPlanMetricsSet,
/// Cache holding plan properties like equivalences, output partitioning
etc.
cache: PlanProperties,
+ /// Null matching behavior: If `null_equals_null` is true, rows that have
+ /// `null`s in both left and right equijoin columns will be matched.
+ /// Otherwise, rows that have `null`s in the join columns will not be
+ /// matched and thus will not appear in the output.
+ null_equals_null: bool,
+ /// Set of equijoin columns from the relations: `(left_col, right_col)`
+ ///
+ /// This is optional as a nested loop join can be passed a 'on' clause
+ /// in the case that a Hash Join cost is more expensive than a
+ /// nested loop join or when a user would like to pick nested loop
+ /// join by hint
+ on: Option<Vec<(PhysicalExprRef, PhysicalExprRef)>>,
Review Comment:
I missed that we may convert EXCEPT to a null aware join. Sorry for that.
If null_equal_null is true, we can replace `=` in the ON clause with `<=>`
and merge it into the filter in the planner. Otherwise, we merge the ON clause
into the filter directly.
> how were you able to have the query use a nested loop join with a on
condition?
There's **no equal(`=` not `<=>`) join condition in `on`,** so the planner
choose nlj
https://github.com/apache/datafusion/blob/e5f596b59ece71329635d41fd7f147d1d702e49e/datafusion/core/src/physical_planner.rs#L1104-L1111
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