mihaibudiu commented on code in PR #4354:
URL: https://github.com/apache/calcite/pull/4354#discussion_r2069719827
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core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java:
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@@ -1227,6 +1227,16 @@ private void substituteSubQuery(Blackboard bb, SubQuery
subQuery) {
// Otherwise, let convertExists translate
// values list into an inline table for the
// reference to Q below.
+ } else if (query instanceof SqlSelect) {
+ // During JOIN ON condition processing, bb.root is
+ // initially null but subquery expansion requires
+ // a non-null bb.root. For IN/NOT IN subqueries
+ // processed via convertExists, we use the join's
+ // left input as bb.root. Exception: in UPDATE queries,
+ // bb.inputs remains null and subquery rewriting is skipped.
+ if (bb.inputs != null && bb.inputs.size() == 2) {
Review Comment:
Yes, but the docs say that the root cannot be a join.
I am wondering about the case when the left input of the join is a join.
Maybe you can at least `assert !(root instanceof Join)` after the assignment?
Moreover, directly assigning to root is strange, I have never seen this
pattern in Calcite.
I would have expected a use of setRoot.
It is true that there is another example in this file, and that code was
written by @julianhyde.
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