1 files changed, 136 insertions, 0 deletions
diff --git a/src/backend/executor/execScan.c b/src/backend/executor/execScan.c
new file mode 100644
index 00000000000..96dd5551289
--- /dev/null
+++ b/src/backend/executor/execScan.c
@@ -0,0 +1,136 @@
+/*-------------------------------------------------------------------------
+ *
+ * execScan.c--
+ *    This code provides support for generalized relation scans. ExecScan
+ *    is passed a node and a pointer to a function to "do the right thing"
+ *    and return a tuple from the relation. ExecScan then does the tedious
+ *    stuff - checking the qualification and projecting the tuple
+ *    appropriately.
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *    $Header: /cvsroot/pgsql/src/backend/executor/execScan.c,v 1.1.1.1 1996/07/09 06:21:25 scrappy Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include <sys/file.h>
+#include "executor/executor.h"
+
+/* ----------------------------------------------------------------
+ *   	ExecScan
+ *   
+ *   	Scans the relation using the 'access method' indicated and 
+ *   	returns the next qualifying tuple in the direction specified
+ *   	in the global variable ExecDirection.
+ *   	The access method returns the next tuple and execScan() is 
+ *   	responisble for checking the tuple returned against the qual-clause.
+ *   	
+ *   	Conditions:
+ *   	  -- the "cursor" maintained by the AMI is positioned at the tuple
+ *   	     returned previously.
+ *   
+ *   	Initial States:
+ *   	  -- the relation indicated is opened for scanning so that the 
+ *   	     "cursor" is positioned before the first qualifying tuple.
+ *
+ *	May need to put startmmgr  and endmmgr in here.
+ * ----------------------------------------------------------------
+ */
+TupleTableSlot *
+ExecScan(Scan *node, 
+	 TupleTableSlot* (*accessMtd)())	/* function returning a tuple */
+{
+    CommonScanState	*scanstate;
+    EState		*estate;
+    List		*qual;
+    bool		isDone;
+
+    TupleTableSlot	*slot;
+    TupleTableSlot	*resultSlot;
+    HeapTuple 		newTuple;
+
+    ExprContext		*econtext;
+    ProjectionInfo	*projInfo;
+
+
+    /* ----------------
+     *	initialize misc variables
+     * ----------------
+     */
+    newTuple = 	NULL;
+    slot =	NULL;
+
+    estate = 	node->plan.state;
+    scanstate =     	node->scanstate;
+
+    /* ----------------
+     *	get the expression context
+     * ----------------
+     */
+    econtext = 	scanstate->cstate.cs_ExprContext;
+
+    /* ----------------
+     *	initialize fields in ExprContext which don't change
+     *	in the course of the scan..
+     * ----------------
+     */
+    qual = node->plan.qual;
+    econtext->ecxt_relation = scanstate->css_currentRelation;
+    econtext->ecxt_relid = node->scanrelid;
+
+    if (scanstate->cstate.cs_TupFromTlist) {
+	projInfo = scanstate->cstate.cs_ProjInfo;
+	resultSlot = ExecProject(projInfo, &isDone);
+	if (!isDone)
+	  return resultSlot;
+    }
+    /* 
+     * get a tuple from the access method 
+     * loop until we obtain a tuple which passes the qualification.
+     */
+    for(;;) {
+	slot = (TupleTableSlot *) (*accessMtd)(node);
+
+	/* ----------------
+	 *  if the slot returned by the accessMtd contains
+	 *  NULL, then it means there is nothing more to scan
+	 *  so we just return the empty slot.
+	 * ----------------
+	 */
+	if (TupIsNull(slot)) return slot;
+	
+	/* ----------------
+	 *   place the current tuple into the expr context
+	 * ----------------
+	 */
+	econtext->ecxt_scantuple = slot;
+	
+	/* ----------------
+	 *  check that the current tuple satisfies the qual-clause
+	 *  if our qualification succeeds then we
+	 *  leave the loop.
+	 * ----------------
+	 */
+
+	/* add a check for non-nil qual here to avoid a
+	   function call to ExecQual() when the qual is nil */
+	if (!qual || ExecQual(qual, econtext) == true)
+	    break;
+    }
+
+    /* ----------------
+     *	form a projection tuple, store it in the result tuple
+     *  slot and return it.
+     * ----------------
+     */
+    projInfo = scanstate->cstate.cs_ProjInfo;
+
+    resultSlot = ExecProject(projInfo, &isDone);
+    scanstate->cstate.cs_TupFromTlist = !isDone;
+
+    return resultSlot;
+}
+