From 42e83449476b5adbdd24ca9a093e10840cc47f79 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Fri, 3 Jan 2025 15:09:06 +0800
Subject: [PATCH v1 1/1] refactoring svariableStartupReceiver

---
 src/backend/executor/svariableReceiver.c | 66 ++++--------------------
 1 file changed, 9 insertions(+), 57 deletions(-)

diff --git a/src/backend/executor/svariableReceiver.c b/src/backend/executor/svariableReceiver.c
index c4cff44ecf..a3574b4685 100644
--- a/src/backend/executor/svariableReceiver.c
+++ b/src/backend/executor/svariableReceiver.c
@@ -28,19 +28,16 @@
 /*
  * This DestReceiver is used by the LET command for storing the result to a
  * session variable.  The result has to have only one tuple with only one
- * non-deleted attribute.  The row counter (field "rows") is incremented
+ * attribute.  The row counter (field "rows") is incremented
  * after receiving a row, and an error is raised when there are no rows or
- * there are more than one received rows.  Because a received tuple can have
- * deleted attributes, we need to find the first non-deleted attribute
- * (field "slot_offset").  The value is detoasted before storing it in the
- * session variable.
+ * there are more than one received rows.
+ * The value is detoasted before storing it in the session variable.
  */
 typedef struct
 {
 	DestReceiver pub;
 	Oid			varid;
 	bool		need_detoast;		/* do we need to detoast the attribute? */
-	int			slot_offset;		/* position of non-deleted attribute */
 	int			rows;				/* row counter */
 } SVariableState;
 
@@ -52,8 +49,7 @@ svariableStartupReceiver(DestReceiver *self, int operation, TupleDesc typeinfo)
 {
 	SVariableState *myState = (SVariableState *) self;
 	int			natts = typeinfo->natts;
-	int			outcols = 0;
-	int			i;
+	Form_pg_attribute attr;
 	LOCKTAG		locktag PG_USED_FOR_ASSERTS_ONLY;
 
 	Assert(myState->pub.mydest == DestVariable);
@@ -71,53 +67,9 @@ svariableStartupReceiver(DestReceiver *self, int operation, TupleDesc typeinfo)
 	Assert(LockHeldByMe(&locktag, AccessShareLock, false));
 
 #endif
-
-	for (i = 0; i < natts; i++)
-	{
-		Form_pg_attribute attr = TupleDescAttr(typeinfo, i);
-		Oid			typid;
-		Oid			collid;
-		int32		typmod;
-
-		if (attr->attisdropped)
-			continue;
-
-		if (++outcols > 1)
-			continue;
-
-		get_session_variable_type_typmod_collid(myState->varid,
-												&typid,
-												&typmod,
-												&collid);
-
-		/*
-		 * Double check - the type and typmod of target variable should be the
-		 * same as the type and typmod of assignment expression.  The
-		 * expression should be wrapped by a cast to the target type/typmod.
-		 */
-		if (attr->atttypid != typid ||
-			(attr->atttypmod >= 0 &&
-			 attr->atttypmod != typmod))
-			ereport(ERROR,
-					(errcode(ERRCODE_DATATYPE_MISMATCH),
-					 errmsg("target session variable is of type %s"
-							" but expression is of type %s",
-							format_type_with_typemod(typid, typmod),
-							format_type_with_typemod(attr->atttypid,
-													 attr->atttypmod))));
-
-		myState->need_detoast = attr->attlen == -1;
-		myState->slot_offset = i;
-	}
-
-	if (outcols != 1)
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg_plural("assignment expression returned %d column",
-							   "assignment expression returned %d columns",
-							   outcols,
-							   outcols)));
-
+	Assert(natts == 1);
+	attr = TupleDescAttr(typeinfo, 0);
+	myState->need_detoast = attr->attlen == -1;
 	myState->rows = 0;
 }
 
@@ -135,8 +87,8 @@ svariableReceiveSlot(TupleTableSlot *slot, DestReceiver *self)
 	/* make sure the tuple is fully deconstructed */
 	slot_getallattrs(slot);
 
-	value = slot->tts_values[myState->slot_offset];
-	isnull = slot->tts_isnull[myState->slot_offset];
+	value = slot->tts_values[0];
+	isnull = slot->tts_isnull[0];
 
 	if (myState->need_detoast && !isnull && VARATT_IS_EXTERNAL(DatumGetPointer(value)))
 	{
-- 
2.34.1