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Disable decorrelation for count() with no grouping columns #1310

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Disable decorrelation for count() with no grouping columns #1310

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9 changes: 8 additions & 1 deletion src/backend/gporca/libgpopt/src/xforms/CDecorrelator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -426,7 +426,14 @@ CDecorrelator::FProcessGbAgg(CMemoryPool *mp, CExpression *pexpr,
return false;
}

// TODO: 12/20/2012 - ; check for strictness of agg function
if (0 == popAggOriginal->Pdrgpcr()->Size())
{
CColRef *pcrCount = nullptr;
if (CUtils::FHasCountAgg((*pexpr)[1], &pcrCount))
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It's OK to process count star and count any here. But it's a general problem, namely, any AggFunc with not nulll initval we should process here.

{
return false;
}
}

// decorrelate relational child, allow only equality predicates, see below for the reason
CExpression *pexprRelational = nullptr;
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35 changes: 12 additions & 23 deletions src/backend/gporca/libgpopt/src/xforms/CSubqueryHandler.cpp
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Expand Up @@ -753,8 +753,7 @@ CSubqueryHandler::FCreateOuterApplyForScalarSubquery(
*ppexprNewOuter = pexprPrj;

BOOL fGeneratedByQuantified = popSubquery->FGeneratedByQuantified();
if (fGeneratedByQuantified ||
(fHasCountAggMatchingColumn && 0 == pgbAgg->Pdrgpcr()->Size()))
if (fGeneratedByQuantified)
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And please add a test case, thanks!

{
CMDAccessor *md_accessor = COptCtxt::PoctxtFromTLS()->Pmda();
const IMDTypeInt8 *pmdtypeint8 = md_accessor->PtMDType<IMDTypeInt8>();
Expand All @@ -765,27 +764,17 @@ CSubqueryHandler::FCreateOuterApplyForScalarSubquery(
CUtils::PexprScalarIdent(mp, pcrComputed),
CUtils::PexprScalarConstInt8(mp, 0 /*val*/));

if (fGeneratedByQuantified)
{
// we produce Null if count(*) value is -1,
// this case can only occur when transforming quantified subquery to
// count(*) subquery using CXformSimplifySubquery
pmdidInt8->AddRef();
*ppexprResidualScalar = GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CScalarIf(mp, pmdidInt8),
CUtils::PexprScalarEqCmp(
mp, pcrComputed,
CUtils::PexprScalarConstInt8(mp, -1 /*value*/)),
CUtils::PexprScalarConstInt8(mp, 0 /*value*/, true /*is_null*/),
pexprCoalesce);
}
else
{
// count(*) value can either be NULL (if produced by a lower outer join), or some value >= 0,
// we return coalesce(count(*), 0) in this case

*ppexprResidualScalar = pexprCoalesce;
}
// we produce Null if count(*) value is -1,
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Why we change logic here?

// this case can only occur when transforming quantified subquery to
// count(*) subquery using CXformSimplifySubquery
pmdidInt8->AddRef();
*ppexprResidualScalar = GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CScalarIf(mp, pmdidInt8),
CUtils::PexprScalarEqCmp(
mp, pcrComputed,
CUtils::PexprScalarConstInt8(mp, -1 /*value*/)),
CUtils::PexprScalarConstInt8(mp, 0 /*value*/, true /*is_null*/),
pexprCoalesce);

return fSuccess;
}
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