jiangzhx commented on PR #5907:
URL:
https://github.com/apache/arrow-datafusion/pull/5907#issuecomment-1513437056
> I will take a look. Usually, for un-correlated scalar subqueries, it will
be kept as the subquery but need to do count check.
>
> WHERE EXISTS (SELECT b FROM t2 where a>1 )
>
> rewrite to
>
> WHERE ScalarSubQuery(SELECT b FROM t2 where a>1 limit 1)
>
> We need to add a physical SubQueryExec.
yes，you are right,as you expressed, in Spark, rewriting `exists` to `scalar
subquery` can solve the query requirements for this scenario.
```
/**
* Rewrite non correlated exists subquery to use ScalarSubquery
* WHERE EXISTS (SELECT A FROM TABLE B WHERE COL1 > 10)
* will be rewritten to
* WHERE (SELECT 1 FROM (SELECT A FROM TABLE B WHERE COL1 > 10) LIMIT 1)
IS NOT NULL
*/
object RewriteNonCorrelatedExists extends Rule[LogicalPlan] {
override def apply(plan: LogicalPlan): LogicalPlan =
plan.transformAllExpressionsWithPruning(
_.containsPattern(EXISTS_SUBQUERY)) {
case exists: Exists if exists.children.isEmpty =>
IsNotNull(
ScalarSubquery(
plan = Limit(Literal(1), Project(Seq(Alias(Literal(1), "col")()),
exists.plan)),
exprId = exists.exprId,
hint = exists.hint))
}
}
```
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