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/*-------------------------------------------------------------------------
*
* nodeUnique.c
* Routines to handle unique'ing of queries where appropriate
*
* Unique is a very simple node type that just filters out duplicate
* tuples from a stream of sorted tuples from its subplan. It's essentially
* a dumbed-down form of Group: the duplicate-removal functionality is
* identical. However, Unique doesn't do projection nor qual checking,
* so it's marginally more efficient for cases where neither is needed.
* (It's debatable whether the savings justifies carrying two plan node
* types, though.)
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/executor/nodeUnique.c
*
*-------------------------------------------------------------------------
*/
/*
* INTERFACE ROUTINES
* ExecUnique - generate a unique'd temporary relation
* ExecInitUnique - initialize node and subnodes
* ExecEndUnique - shutdown node and subnodes
*
* NOTES
* Assumes tuples returned from subplan arrive in
* sorted order.
*/
#include "postgres.h"
#include "executor/executor.h"
#include "executor/nodeUnique.h"
#include "miscadmin.h"
#include "utils/memutils.h"
/* ----------------------------------------------------------------
* ExecUnique
* ----------------------------------------------------------------
*/
static TupleTableSlot * /* return: a tuple or NULL */
ExecUnique(PlanState *pstate)
{
UniqueState *node = castNode(UniqueState, pstate);
ExprContext *econtext = node->ps.ps_ExprContext;
TupleTableSlot *resultTupleSlot;
TupleTableSlot *slot;
PlanState *outerPlan;
CHECK_FOR_INTERRUPTS();
/*
* get information from the node
*/
outerPlan = outerPlanState(node);
resultTupleSlot = node->ps.ps_ResultTupleSlot;
/*
* now loop, returning only non-duplicate tuples. We assume that the
* tuples arrive in sorted order so we can detect duplicates easily. The
* first tuple of each group is returned.
*/
for (;;)
{
/*
* fetch a tuple from the outer subplan
*/
slot = ExecProcNode(outerPlan);
if (TupIsNull(slot))
{
/* end of subplan, so we're done */
ExecClearTuple(resultTupleSlot);
return NULL;
}
/*
* Always return the first tuple from the subplan.
*/
if (TupIsNull(resultTupleSlot))
break;
/*
* Else test if the new tuple and the previously returned tuple match.
* If so then we loop back and fetch another new tuple from the
* subplan.
*/
econtext->ecxt_innertuple = slot;
econtext->ecxt_outertuple = resultTupleSlot;
if (!ExecQualAndReset(node->eqfunction, econtext))
break;
}
/*
* We have a new tuple different from the previous saved tuple (if any).
* Save it and return it. We must copy it because the source subplan
* won't guarantee that this source tuple is still accessible after
* fetching the next source tuple.
*/
return ExecCopySlot(resultTupleSlot, slot);
}
/* ----------------------------------------------------------------
* ExecInitUnique
*
* This initializes the unique node state structures and
* the node's subplan.
* ----------------------------------------------------------------
*/
UniqueState *
ExecInitUnique(Unique *node, EState *estate, int eflags)
{
UniqueState *uniquestate;
/* check for unsupported flags */
Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
/*
* create state structure
*/
uniquestate = makeNode(UniqueState);
uniquestate->ps.plan = (Plan *) node;
uniquestate->ps.state = estate;
uniquestate->ps.ExecProcNode = ExecUnique;
/*
* create expression context
*/
ExecAssignExprContext(estate, &uniquestate->ps);
/*
* then initialize outer plan
*/
outerPlanState(uniquestate) = ExecInitNode(outerPlan(node), estate, eflags);
/*
* Initialize result slot and type. Unique nodes do no projections, so
* initialize projection info for this node appropriately.
*/
ExecInitResultTupleSlotTL(&uniquestate->ps, &TTSOpsMinimalTuple);
uniquestate->ps.ps_ProjInfo = NULL;
/*
* Precompute fmgr lookup data for inner loop
*/
uniquestate->eqfunction =
execTuplesMatchPrepare(ExecGetResultType(outerPlanState(uniquestate)),
node->numCols,
node->uniqColIdx,
node->uniqOperators,
node->uniqCollations,
&uniquestate->ps);
return uniquestate;
}
/* ----------------------------------------------------------------
* ExecEndUnique
*
* This shuts down the subplan and frees resources allocated
* to this node.
* ----------------------------------------------------------------
*/
void
ExecEndUnique(UniqueState *node)
{
/* clean up tuple table */
ExecClearTuple(node->ps.ps_ResultTupleSlot);
ExecFreeExprContext(&node->ps);
ExecEndNode(outerPlanState(node));
}
void
ExecReScanUnique(UniqueState *node)
{
/* must clear result tuple so first input tuple is returned */
ExecClearTuple(node->ps.ps_ResultTupleSlot);
/*
* if chgParam of subnode is not null then plan will be re-scanned by
* first ExecProcNode.
*/
if (node->ps.lefttree->chgParam == NULL)
ExecReScan(node->ps.lefttree);
}
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