pratham76 commented on code in PR #58656:
URL: https://github.com/apache/spark/pull/58656#discussion_r4056573515
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/subquery.scala:
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@@ -450,10 +471,100 @@ object RewritePredicateSubquery extends
Rule[LogicalPlan] with PredicateHelper {
ExistenceJoin(exists), newConditions, joinHint)
introducedAttrs += exists
exists
+ // A sub-query that `canRewrite` declined is left as it is, children
included.
+ case sq @ (_: Exists | Not(_: InSubquery) | _: InSubquery) => sq
+ case other => other.mapChildren(rewrite)
}
}
+ val newExprs = exprs.map(rewrite)
(newExprs.reduceOption(And), newPlan, introducedAttrs.toSeq)
}
+
+ /**
+ * Returns true if `e` references any of the attributes produced by `plan`.
+ */
+ private def referencesPlan(e: Expression, plan: LogicalPlan): Boolean = {
+ e.references.intersect(plan.outputSet).nonEmpty
+ }
+
+ /**
+ * Rewrites the existential sub-queries that are nested in the correlated
predicates which
+ * [[PullupCorrelatedPredicates]] hoisted out of a predicate sub-query, and
which therefore end
+ * up in the condition of the semi/anti join that replaces that sub-query.
+ *
+ * A hoisted predicate can carry a nested existential sub-query out of the
sub-query plan,
+ * because a correlated predicate is hoisted as a whole when it is a
disjunction. For example
+ *
+ * SELECT * FROM t1 WHERE EXISTS (
+ * SELECT 1 FROM t2 WHERE t1.a = t2.c1 OR t2.c1 IN (SELECT col1 FROM t3))
+ *
+ * hoists `a = c1 OR c1 IN (SELECT col1 FROM t3)` into the join condition.
Such a nested
+ * sub-query must be rewritten against the plan that produces the attributes
it references:
+ * the one above references `c1`, which is produced by the sub-query plan
and not by the outer
+ * plan, so its existence join has to be built on top of the sub-query plan.
Building it on top
+ * of the outer plan instead yields a join whose condition references an
attribute that neither
+ * of its children can produce (SPARK-59351).
+ *
+ * A nested sub-query that references both plans cannot be rewritten into an
existence join on
+ * either side, so it is left in the join condition, where both plans are in
scope. This is only
+ * correct for an uncorrelated sub-query: the join condition of a correlated
one is dropped when
+ * it is planned as an in-subquery filter, which would silently change the
result, so it is
+ * reported as unsupported instead. Note that such a sub-query can be
correlated only to the
+ * sub-query plan, as being correlated to the outer plan as well would
require two levels of
+ * correlation, which the Analyzer rejects.
+ *
+ * Returns the rewritten condition along with the updated outer and
sub-query plans.
+ */
+ private def rewriteExistentialExprInJoinCondition(
+ conditions: Seq[Expression],
+ outerPlan: LogicalPlan,
+ subPlan: LogicalPlan): (Option[Expression], LogicalPlan, LogicalPlan) = {
+ val (subCond, newSubPlan) =
+ rewriteExistentialExprInSubqueryPlan(conditions, outerPlan, subPlan)
+ // The sub-queries that do not reference the sub-query plan are rewritten
against the outer
+ // plan, as they only reference attributes of the outer plan, if any.
+ val (newCond, newOuterPlan, _) = rewriteExistentialExprWithAttrs(
+ subCond.toSeq, outerPlan, e => !referencesPlan(e, subPlan))
+ (newCond, newOuterPlan, newSubPlan)
+ }
+
+ /**
+ * Rewrites the existential sub-queries in `conditions` that can only be
evaluated by the
+ * sub-query plan, that is those referencing the sub-query plan but not the
outer plan, into
+ * existence joins on top of the sub-query plan. See
+ * [[rewriteExistentialExprInJoinCondition]] for details.
+ *
+ * Returns the rewritten condition along with the updated sub-query plan.
+ */
+ private def rewriteExistentialExprInSubqueryPlan(
+ conditions: Seq[Expression],
+ outerPlan: LogicalPlan,
+ subPlan: LogicalPlan): (Option[Expression], LogicalPlan) = {
+ // A correlated sub-query referencing both plans has to stay in the join
condition, where its
+ // own join condition is lost, so reject it rather than silently return a
wrong result.
+ val unsupported = conditions.flatMap(_.collect {
+ case sq @ (_: Exists | _: InSubquery)
+ if isCorrelatedSubquery(sq) &&
+ referencesPlan(sq, subPlan) && referencesPlan(sq, outerPlan) => sq
+ })
+ if (unsupported.nonEmpty) {
+ throw
QueryCompilationErrors.unsupportedCorrelatedSubqueryInJoinConditionError(unsupported)
Review Comment:
Agreed — "join predicate" and "join inputs" name nothing in a query whose
SQL contains no join.
Rather than reword the existing sub-condition, which is right for the site
at `subquery.scala:249`
where the user did write a JOIN, this adds two sibling sub-conditions under
the same `0A000`
category and uses them at the new sites:
* `NESTED_SUBQUERY_REFERENCING_OUTER_AND_INNER_QUERY` — "The subquery
`<subqueryExpression>` is
nested in a correlated condition of another subquery, and references both
the outer query and the
subquery it is nested in."
* `NESTED_IN_SUBQUERY_WITH_UNKNOWN_RESULT` — "The IN subquery
`<subqueryExpression>` is nested in a
correlated condition of another subquery, and its result can be unknown
where it is not used as a
predicate."
The existing sub-condition keeps its JOIN wording and its call site. Names
and wording are of course
open to your preference.
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