greenplumn CXformSimplifyLeftOuterJoin 代码
文件路径：/src/backend/gporca/libgpopt/src/xforms/CXformSimplifyLeftOuterJoin.cpp
/---------------------------------------------------------------------------
/ Greenplum Database
/ Copyright (C) 2013 EMC Corp.
/
/ @filename:
/ CXformSimplifyLeftOuterJoin.cpp
/
/ @doc:
/ Simplify Left Outer Join with constant false predicate
/---------------------------------------------------------------------------
#include "gpopt/xforms/CXformSimplifyLeftOuterJoin.h"
#include "gpos/base.h"
#include "gpopt/base/CUtils.h"
#include "gpopt/operators/CLogicalConstTableGet.h"
#include "gpopt/operators/CLogicalLeftOuterJoin.h"
#include "gpopt/operators/CPatternLeaf.h"
#include "gpopt/operators/CPatternTree.h"
using namespace gpmd;
using namespace gpopt;
/---------------------------------------------------------------------------
/ @function:
/ CXformSimplifyLeftOuterJoin::CXformSimplifyLeftOuterJoin
/
/ @doc:
/ Ctor
/
/---------------------------------------------------------------------------
CXformSimplifyLeftOuterJoin::CXformSimplifyLeftOuterJoin(CMemoryPool *mp)
: CXformExploration(
/ pattern
GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CLogicalLeftOuterJoin(mp),
GPOS_NEW(mp)
CExpression(mp, GPOS_NEW(mp) CPatternLeaf(mp)), / left child
GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CPatternLeaf(mp)), / right child
GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CPatternTree(mp)) / predicate tree
))
{
}
/---------------------------------------------------------------------------
/ @function:
/ CXformSimplifyLeftOuterJoin::Exfp
/
/ @doc:
/ Compute xform promise for a given expression handle
/
/---------------------------------------------------------------------------
CXform::EXformPromise
CXformSimplifyLeftOuterJoin::Exfp(CExpressionHandle &exprhdl) const
{
CExpression *pexprScalar = exprhdl.PexprScalarExactChild(2 /*child_index*/);
if (nullptr != pexprScalar && CUtils::FScalarConstFalse(pexprScalar))
{
/ if LOJ predicate is False, we can replace inner child with empty table
return CXform::ExfpHigh;
}
return CXform::ExfpNone;
}
/---------------------------------------------------------------------------
/ @function:
/ CXformSimplifyLeftOuterJoin::Transform
/
/ @doc:
/ Actual transformation to simplify left outer join
/
/---------------------------------------------------------------------------
void
CXformSimplifyLeftOuterJoin::Transform(CXformContext *pxfctxt,
CXformResult *pxfres,
CExpression *pexpr) const
{
GPOS_ASSERT(nullptr != pxfctxt);
GPOS_ASSERT(nullptr != pxfres);
GPOS_ASSERT(FPromising(pxfctxt->Pmp(), this, pexpr));
GPOS_ASSERT(FCheckPattern(pexpr));
CMemoryPool *mp = pxfctxt->Pmp();
/ extract components
CExpression *pexprOuter = (*pexpr)[0];
CExpression *pexprInner = (*pexpr)[1];
CExpression *pexprScalar = (*pexpr)[2];
pexprOuter->AddRef();
pexprScalar->AddRef();
CExpression *pexprResult = nullptr;
/ inner child of LOJ can be replaced with empty table
GPOS_ASSERT(CUtils::FScalarConstFalse(pexprScalar));
/ extract output columns of inner child
CColRefArray *colref_array = pexprInner->DeriveOutputColumns()->Pdrgpcr(mp);
/ generate empty constant table with the same columns
COperator *popCTG = GPOS_NEW(mp)
CLogicalConstTableGet(mp, colref_array, GPOS_NEW(mp) IDatum2dArray(mp));
pexprResult = GPOS_NEW(mp)
CExpression(mp, GPOS_NEW(mp) CLogicalLeftOuterJoin(mp), pexprOuter,
GPOS_NEW(mp) CExpression(mp, popCTG), pexprScalar);
pxfres->Add(pexprResult);
}
/ EOF
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