Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/9055#discussion_r42585365
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -270,6 +273,146 @@ class Analyzer(
}
/**
+ * Rewrite the [[Exists]] [[In]] with left semi join or anti join.
+ */
+ object RewriteFilterSubQuery extends Rule[LogicalPlan] with
PredicateHelper {
+ def unapply(condition: Expression): Option[(Expression,
Seq[Expression])] = {
+ if (condition.resolved == false) {
+ return None
+ }
+
+ val conjuctions = splitConjunctivePredicates(condition).map(_
transformDown {
+ // Remove the Cast expression for SubQueryExpression.
+ case Cast(f: SubQueryExpression, BooleanType) => f
+ }
+ )
+
+ val (subqueries, others) = conjuctions.partition(c =>
c.isInstanceOf[SubQueryExpression])
+ if (subqueries.isEmpty) {
+ None
+ } else if (subqueries.length > 1) {
+ throw new AnalysisException(
+ s"Only 1 SubQuery expression is supported, but we got
$subqueries")
+ } else {
+ val subQueryExpr = subqueries(0).asInstanceOf[SubQueryExpression]
+ // try to resolve the subquery
+
+ val subquery = Analyzer.this.execute(subQueryExpr.subquery) match {
+ case Distinct(child) => child // Distinct is useless for semi
join, ignore it.
+ case other => other
+ }
+ Some((subQueryExpr.withNewSubQuery(subquery), others))
+ }
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
+ case f if f.childrenResolved == false => f
+
+ case f @ Filter(RewriteFilterSubQuery(subquery, others), left) =>
+ subquery match {
+ case Exists(Project(_, Filter(condition, right)), positive) =>
+ checkAnalysis(right)
+ if (condition.resolved) {
+ // Apparently, it should be not resolved here, since EXIST
should be correlated.
+ throw new AnalysisException(
+ s"Exist clause should be correlated, but we got
$condition")
+ }
+ Join(others.reduceOption(And).map(Filter(_,
left)).getOrElse(left), right,
+ if (positive) LeftSemi else LeftAnti,
+ Some(ResolveReferences.tryResolveAttributes(condition,
right)))
+
+ case Exists(right, positive) =>
+ throw new AnalysisException(s"Exist clause should be
correlated, but we got $right")
+
+ case InSubquery(key, Project(projectList, Filter(condition,
right)), positive) =>
+ checkAnalysis(right)
+ if (projectList.length != 1) {
+ throw new AnalysisException(
+ s"Expect only 1 projection in In Subquery Expression, but
we got $projectList")
+ } else {
+ val rightKey =
ResolveReferences.tryResolveAttributes(projectList(0), right)
--- End diff --
This is a good question, actually this is a workaround to solve the
ambiguous references issue like:.
`SELECT 'value FROM src WHERE 'key IN (SELECT 'key FROM src b WHERE 'key >
100)`
Literally, we will transform the SQL as:
`SELECT 'value FROM src LEFT SEMI JOIN src b ON 'key = 'key and 'key >
100`, this is reference ambiguous for `'key`!
The `ResolveReferences.tryResolveAttributes` will partially resolve the
project list and filter condition of the subquery, and then what we got looks
like:
`SELECT 'value FROM src LEFI SEMI JOIN src b ON 'key = key#123 and key#123
> 100`
And then we will leave the unresolved attributes for the other rules.
There is another doable solution is complete the alias for the attributes /
relations like first:
`SELECT 'value FROM src WHERE 'key IN (SELECT 'key FROM src b WHERE 'key >
100)` =>
`SELECT 'a.value FROM src a WHERE 'a.key IN (SELECT 'b.key FROM src b WHERE
'b.key > 100)` =>
`SELECT 'a.value FROM src a LEFT SEMI JOIN src b ON 'a.key = 'b.key and
'b.key > 100`
But this probably requires more code change, and probably will confusing
people when they check the generated logical plan.
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