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146 lines
4.2 KiB
C
146 lines
4.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* execScan.c
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* This code provides support for generalized relation scans. ExecScan
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* is passed a node and a pointer to a function to "do the right thing"
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* and return a tuple from the relation. ExecScan then does the tedious
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* stuff - checking the qualification and projecting the tuple
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* appropriately.
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*
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* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/executor/execScan.c,v 1.18 2001/10/25 05:49:27 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include <sys/types.h>
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#include <sys/file.h>
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#include "postgres.h"
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#include "executor/executor.h"
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#include "utils/memutils.h"
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/* ----------------------------------------------------------------
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* ExecScan
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*
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* Scans the relation using the 'access method' indicated and
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* returns the next qualifying tuple in the direction specified
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* in the global variable ExecDirection.
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* The access method returns the next tuple and execScan() is
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* responsible for checking the tuple returned against the qual-clause.
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*
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* Conditions:
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* -- the "cursor" maintained by the AMI is positioned at the tuple
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* returned previously.
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*
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* Initial States:
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* -- the relation indicated is opened for scanning so that the
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* "cursor" is positioned before the first qualifying tuple.
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* ----------------------------------------------------------------
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*/
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TupleTableSlot *
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ExecScan(Scan *node,
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ExecScanAccessMtd accessMtd) /* function returning a tuple */
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{
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CommonScanState *scanstate;
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EState *estate;
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ExprContext *econtext;
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List *qual;
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ExprDoneCond isDone;
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TupleTableSlot *resultSlot;
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/*
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* Fetch data from node
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*/
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estate = node->plan.state;
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scanstate = node->scanstate;
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econtext = scanstate->cstate.cs_ExprContext;
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qual = node->plan.qual;
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/*
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* Check to see if we're still projecting out tuples from a previous
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* scan tuple (because there is a function-returning-set in the
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* projection expressions). If so, try to project another one.
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*/
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if (scanstate->cstate.cs_TupFromTlist)
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{
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resultSlot = ExecProject(scanstate->cstate.cs_ProjInfo, &isDone);
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if (isDone == ExprMultipleResult)
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return resultSlot;
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/* Done with that source tuple... */
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scanstate->cstate.cs_TupFromTlist = false;
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}
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/*
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* Reset per-tuple memory context to free any expression evaluation
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* storage allocated in the previous tuple cycle. Note this can't
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* happen until we're done projecting out tuples from a scan tuple.
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*/
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ResetExprContext(econtext);
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/*
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* get a tuple from the access method loop until we obtain a tuple
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* which passes the qualification.
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*/
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for (;;)
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{
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TupleTableSlot *slot;
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slot = (*accessMtd) (node);
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/*
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* if the slot returned by the accessMtd contains NULL, then it
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* means there is nothing more to scan so we just return an empty
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* slot, being careful to use the projection result slot so it has
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* correct tupleDesc.
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*/
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if (TupIsNull(slot))
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{
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return ExecStoreTuple(NULL,
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scanstate->cstate.cs_ProjInfo->pi_slot,
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InvalidBuffer,
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true);
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}
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/*
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* place the current tuple into the expr context
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*/
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econtext->ecxt_scantuple = slot;
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/*
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* check that the current tuple satisfies the qual-clause
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*
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* check for non-nil qual here to avoid a function call to ExecQual()
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* when the qual is nil ... saves only a few cycles, but they add
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* up ...
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*/
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if (!qual || ExecQual(qual, econtext, false))
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{
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/*
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* Found a satisfactory scan tuple.
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*
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* Form a projection tuple, store it in the result tuple slot and
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* return it --- unless we find we can project no tuples from
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* this scan tuple, in which case continue scan.
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*/
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resultSlot = ExecProject(scanstate->cstate.cs_ProjInfo, &isDone);
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if (isDone != ExprEndResult)
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{
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scanstate->cstate.cs_TupFromTlist = (isDone == ExprMultipleResult);
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return resultSlot;
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}
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}
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/*
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* Tuple fails qual, so free per-tuple memory and try again.
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*/
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ResetExprContext(econtext);
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}
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}
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