nodeGroup.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * nodeGroup.c
 *    Routines to handle group nodes (used for queries with GROUP BY clause).
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * DESCRIPTION
 *    The Group node is designed for handling queries with a GROUP BY clause.
 *    Its outer plan must deliver tuples that are sorted in the order
 *    specified by the grouping columns (ie. tuples from the same group are
 *    consecutive).  That way, we just have to compare adjacent tuples to
 *    locate group boundaries.
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeGroup.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "executor/executor.h"
#include "executor/nodeGroup.h"
#include "miscadmin.h"
#include "utils/memutils.h"
 
 
/*
 *   ExecGroup -
 *
 *      Return one tuple for each group of matching input tuples.
 */
static TupleTableSlot *
ExecGroup(PlanState *pstate)
{
    GroupState *node = castNode(GroupState, pstate);
    ExprContext *econtext;
    TupleTableSlot *firsttupleslot;
    TupleTableSlot *outerslot;
 
    CHECK_FOR_INTERRUPTS();
 
    /*
     * get state info from node
     */
    if (node->grp_done)
        return NULL;
    econtext = node->ss.ps.ps_ExprContext;
 
    /*
     * The ScanTupleSlot holds the (copied) first tuple of each group.
     */
    firsttupleslot = node->ss.ss_ScanTupleSlot;
 
    /*
     * We need not call ResetExprContext here because ExecQualAndReset() will
     * reset the per-tuple memory context once per input tuple.
     */
 
    /*
     * If first time through, acquire first input tuple and determine whether
     * to return it or not.
     */
    if (TupIsNull(firsttupleslot))
    {
        outerslot = ExecProcNode(outerPlanState(node));
        if (TupIsNull(outerslot))
        {
            /* empty input, so return nothing */
            node->grp_done = true;
            return NULL;
        }
        /* Copy tuple into firsttupleslot */
        ExecCopySlot(firsttupleslot, outerslot);
 
        /*
         * Set it up as input for qual test and projection.  The expressions
         * will access the input tuple as varno OUTER.
         */
        econtext->ecxt_outertuple = firsttupleslot;
 
        /*
         * Check the qual (HAVING clause); if the group does not match, ignore
         * it and fall into scan loop.
         */
        if (ExecQual(node->ss.ps.qual, econtext))
        {
            /*
             * Form and return a projection tuple using the first input tuple.
             */
            return ExecProject(node->ss.ps.ps_ProjInfo);
        }
        else
            InstrCountFiltered1(node, 1);
    }
 
    /*
     * This loop iterates once per input tuple group.  At the head of the
     * loop, we have finished processing the first tuple of the group and now
     * need to scan over all the other group members.
     */
    for (;;)
    {
        /*
         * Scan over all remaining tuples that belong to this group
         */
        for (;;)
        {
            outerslot = ExecProcNode(outerPlanState(node));
            if (TupIsNull(outerslot))
            {
                /* no more groups, so we're done */
                node->grp_done = true;
                return NULL;
            }
 
            /*
             * Compare with first tuple and see if this tuple is of the same
             * group.  If so, ignore it and keep scanning.
             */
            econtext->ecxt_innertuple = firsttupleslot;
            econtext->ecxt_outertuple = outerslot;
            if (!ExecQualAndReset(node->eqfunction, econtext))
                break;
        }
 
        /*
         * We have the first tuple of the next input group.  See if we want to
         * return it.
         */
        /* Copy tuple, set up as input for qual test and projection */
        ExecCopySlot(firsttupleslot, outerslot);
        econtext->ecxt_outertuple = firsttupleslot;
 
        /*
         * Check the qual (HAVING clause); if the group does not match, ignore
         * it and loop back to scan the rest of the group.
         */
        if (ExecQual(node->ss.ps.qual, econtext))
        {
            /*
             * Form and return a projection tuple using the first input tuple.
             */
            return ExecProject(node->ss.ps.ps_ProjInfo);
        }
        else
            InstrCountFiltered1(node, 1);
    }
}
 
/* -----------------
 * ExecInitGroup
 *
 *  Creates the run-time information for the group node produced by the
 *  planner and initializes its outer subtree
 * -----------------
 */
GroupState *
ExecInitGroup(Group *node, EState *estate, int eflags)
{
    GroupState *grpstate;
    const TupleTableSlotOps *tts_ops;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * create state structure
     */
    grpstate = makeNode(GroupState);
    grpstate->ss.ps.plan = (Plan *) node;
    grpstate->ss.ps.state = estate;
    grpstate->ss.ps.ExecProcNode = ExecGroup;
    grpstate->grp_done = false;
 
    /*
     * create expression context
     */
    ExecAssignExprContext(estate, &grpstate->ss.ps);
 
    /*
     * initialize child nodes
     */
    outerPlanState(grpstate) = ExecInitNode(outerPlan(node), estate, eflags);
 
    /*
     * Initialize scan slot and type.
     */
    tts_ops = ExecGetResultSlotOps(outerPlanState(&grpstate->ss), NULL);
    ExecCreateScanSlotFromOuterPlan(estate, &grpstate->ss, tts_ops);
 
    /*
     * Initialize result slot, type and projection.
     */
    ExecInitResultTupleSlotTL(&grpstate->ss.ps, &TTSOpsVirtual);
    ExecAssignProjectionInfo(&grpstate->ss.ps, NULL);
 
    /*
     * initialize child expressions
     */
    grpstate->ss.ps.qual =
        ExecInitQual(node->plan.qual, (PlanState *) grpstate);
 
    /*
     * Precompute fmgr lookup data for inner loop
     */
    grpstate->eqfunction =
        execTuplesMatchPrepare(ExecGetResultType(outerPlanState(grpstate)),
                               node->numCols,
                               node->grpColIdx,
                               node->grpOperators,
                               node->grpCollations,
                               &grpstate->ss.ps);
 
    return grpstate;
}
 
/* ------------------------
 *      ExecEndGroup(node)
 *
 * -----------------------
 */
void
ExecEndGroup(GroupState *node)
{
    PlanState  *outerPlan;
 
    ExecFreeExprContext(&node->ss.ps);
 
    /* clean up tuple table */
    ExecClearTuple(node->ss.ss_ScanTupleSlot);
 
    outerPlan = outerPlanState(node);
    ExecEndNode(outerPlan);
}
 
void
ExecReScanGroup(GroupState *node)
{
    PlanState  *outerPlan = outerPlanState(node);
 
    node->grp_done = false;
    /* must clear first tuple */
    ExecClearTuple(node->ss.ss_ScanTupleSlot);
 
    /*
     * if chgParam of subnode is not null then plan will be re-scanned by
     * first ExecProcNode.
     */
    if (outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
}