Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * nodeUnique.c
       4             :  *    Routines to handle unique'ing of queries where appropriate
       5             :  *
       6             :  * Unique is a very simple node type that just filters out duplicate
       7             :  * tuples from a stream of sorted tuples from its subplan.  It's essentially
       8             :  * a dumbed-down form of Group: the duplicate-removal functionality is
       9             :  * identical.  However, Unique doesn't do projection nor qual checking,
      10             :  * so it's marginally more efficient for cases where neither is needed.
      11             :  * (It's debatable whether the savings justifies carrying two plan node
      12             :  * types, though.)
      13             :  *
      14             :  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
      15             :  * Portions Copyright (c) 1994, Regents of the University of California
      16             :  *
      17             :  *
      18             :  * IDENTIFICATION
      19             :  *    src/backend/executor/nodeUnique.c
      20             :  *
      21             :  *-------------------------------------------------------------------------
      22             :  */
      23             : /*
      24             :  * INTERFACE ROUTINES
      25             :  *      ExecUnique      - generate a unique'd temporary relation
      26             :  *      ExecInitUnique  - initialize node and subnodes
      27             :  *      ExecEndUnique   - shutdown node and subnodes
      28             :  *
      29             :  * NOTES
      30             :  *      Assumes tuples returned from subplan arrive in
      31             :  *      sorted order.
      32             :  */
      33             : 
      34             : #include "postgres.h"
      35             : 
      36             : #include "executor/executor.h"
      37             : #include "executor/nodeUnique.h"
      38             : #include "miscadmin.h"
      39             : 
      40             : 
      41             : /* ----------------------------------------------------------------
      42             :  *      ExecUnique
      43             :  * ----------------------------------------------------------------
      44             :  */
      45             : static TupleTableSlot *         /* return: a tuple or NULL */
      46      111486 : ExecUnique(PlanState *pstate)
      47             : {
      48      111486 :     UniqueState *node = castNode(UniqueState, pstate);
      49      111486 :     ExprContext *econtext = node->ps.ps_ExprContext;
      50             :     TupleTableSlot *resultTupleSlot;
      51             :     TupleTableSlot *slot;
      52             :     PlanState  *outerPlan;
      53             : 
      54      111486 :     CHECK_FOR_INTERRUPTS();
      55             : 
      56             :     /*
      57             :      * get information from the node
      58             :      */
      59      111486 :     outerPlan = outerPlanState(node);
      60      111486 :     resultTupleSlot = node->ps.ps_ResultTupleSlot;
      61             : 
      62             :     /*
      63             :      * now loop, returning only non-duplicate tuples. We assume that the
      64             :      * tuples arrive in sorted order so we can detect duplicates easily. The
      65             :      * first tuple of each group is returned.
      66             :      */
      67             :     for (;;)
      68             :     {
      69             :         /*
      70             :          * fetch a tuple from the outer subplan
      71             :          */
      72      444516 :         slot = ExecProcNode(outerPlan);
      73      444516 :         if (TupIsNull(slot))
      74             :         {
      75             :             /* end of subplan, so we're done */
      76       14200 :             ExecClearTuple(resultTupleSlot);
      77       14200 :             return NULL;
      78             :         }
      79             : 
      80             :         /*
      81             :          * Always return the first tuple from the subplan.
      82             :          */
      83      430316 :         if (TupIsNull(resultTupleSlot))
      84             :             break;
      85             : 
      86             :         /*
      87             :          * Else test if the new tuple and the previously returned tuple match.
      88             :          * If so then we loop back and fetch another new tuple from the
      89             :          * subplan.
      90             :          */
      91      418842 :         econtext->ecxt_innertuple = slot;
      92      418842 :         econtext->ecxt_outertuple = resultTupleSlot;
      93      418842 :         if (!ExecQualAndReset(node->eqfunction, econtext))
      94       85812 :             break;
      95             :     }
      96             : 
      97             :     /*
      98             :      * We have a new tuple different from the previous saved tuple (if any).
      99             :      * Save it and return it.  We must copy it because the source subplan
     100             :      * won't guarantee that this source tuple is still accessible after
     101             :      * fetching the next source tuple.
     102             :      */
     103       97286 :     return ExecCopySlot(resultTupleSlot, slot);
     104             : }
     105             : 
     106             : /* ----------------------------------------------------------------
     107             :  *      ExecInitUnique
     108             :  *
     109             :  *      This initializes the unique node state structures and
     110             :  *      the node's subplan.
     111             :  * ----------------------------------------------------------------
     112             :  */
     113             : UniqueState *
     114        4790 : ExecInitUnique(Unique *node, EState *estate, int eflags)
     115             : {
     116             :     UniqueState *uniquestate;
     117             : 
     118             :     /* check for unsupported flags */
     119             :     Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
     120             : 
     121             :     /*
     122             :      * create state structure
     123             :      */
     124        4790 :     uniquestate = makeNode(UniqueState);
     125        4790 :     uniquestate->ps.plan = (Plan *) node;
     126        4790 :     uniquestate->ps.state = estate;
     127        4790 :     uniquestate->ps.ExecProcNode = ExecUnique;
     128             : 
     129             :     /*
     130             :      * create expression context
     131             :      */
     132        4790 :     ExecAssignExprContext(estate, &uniquestate->ps);
     133             : 
     134             :     /*
     135             :      * then initialize outer plan
     136             :      */
     137        4790 :     outerPlanState(uniquestate) = ExecInitNode(outerPlan(node), estate, eflags);
     138             : 
     139             :     /*
     140             :      * Initialize result slot and type. Unique nodes do no projections, so
     141             :      * initialize projection info for this node appropriately.
     142             :      */
     143        4790 :     ExecInitResultTupleSlotTL(&uniquestate->ps, &TTSOpsMinimalTuple);
     144        4790 :     uniquestate->ps.ps_ProjInfo = NULL;
     145             : 
     146             :     /*
     147             :      * Precompute fmgr lookup data for inner loop
     148             :      */
     149        4790 :     uniquestate->eqfunction =
     150        4790 :         execTuplesMatchPrepare(ExecGetResultType(outerPlanState(uniquestate)),
     151             :                                node->numCols,
     152        4790 :                                node->uniqColIdx,
     153        4790 :                                node->uniqOperators,
     154        4790 :                                node->uniqCollations,
     155             :                                &uniquestate->ps);
     156             : 
     157        4790 :     return uniquestate;
     158             : }
     159             : 
     160             : /* ----------------------------------------------------------------
     161             :  *      ExecEndUnique
     162             :  *
     163             :  *      This shuts down the subplan and frees resources allocated
     164             :  *      to this node.
     165             :  * ----------------------------------------------------------------
     166             :  */
     167             : void
     168        4790 : ExecEndUnique(UniqueState *node)
     169             : {
     170        4790 :     ExecEndNode(outerPlanState(node));
     171        4790 : }
     172             : 
     173             : 
     174             : void
     175        9728 : ExecReScanUnique(UniqueState *node)
     176             : {
     177        9728 :     PlanState  *outerPlan = outerPlanState(node);
     178             : 
     179             :     /* must clear result tuple so first input tuple is returned */
     180        9728 :     ExecClearTuple(node->ps.ps_ResultTupleSlot);
     181             : 
     182             :     /*
     183             :      * if chgParam of subnode is not null then plan will be re-scanned by
     184             :      * first ExecProcNode.
     185             :      */
     186        9728 :     if (outerPlan->chgParam == NULL)
     187           0 :         ExecReScan(outerPlan);
     188        9728 : }