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From: zfong <git@git.apache.org>
To: dev@drill.apache.org
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References: <git-pr-748-drill@git.apache.org>
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Subject: [GitHub] drill pull request #748: DRILL-5263: Prevent left NLJoin with non scalar sub...
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Message-Id: <20170214171136.E2115DFD73@git1-us-west.apache.org>
Date: Tue, 14 Feb 2017 17:11:36 +0000 (UTC)
archived-at: Tue, 14 Feb 2017 17:11:39 -0000

Github user zfong commented on a diff in the pull request:

    https://github.com/apache/drill/pull/748#discussion_r101089177
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/NestedLoopJoinPrule.java ---
    @@ -49,7 +49,7 @@ protected boolean checkPreconditions(DrillJoinRel join, RelNode left, RelNode ri
           PlannerSettings settings) {
         JoinRelType type = join.getJoinType();
     
    -    if (! (type == JoinRelType.INNER || type == JoinRelType.LEFT)) {
    +    if (!(type == JoinRelType.INNER || (type == JoinRelType.LEFT && JoinUtils.hasScalarSubqueryInput(left, right)))) {
    --- End diff --
    
    I see.  So, Calcite is converting a query with a subquery into an equivalent left join with a scalar subquery.  Do you know if the query returns the correct result in that case if a nested loop join is used?  If not, then it seems like we should still be returning an error.
    
    Also, how do you distinguish the case where the query has been converted to this form by Calcite vs a user explicitly doing a left outer join to a scalar subquery.  It seems like in this case, if Drill uses a nested loop join, it will also return wrong result.


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