From: Tom Lane <tgl@sss.pgh.pa.us>
To: Masahiko Sawada <sawada.mshk@gmail.com>
cc: krking@zju.edu.cn, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17477: A crash bug in transformValuesClause()
In-reply-to: 
 <CAD21AoCF5EWSXUR6MOGUWeqqo5bGw=_4LHDbwhPjO4x+xQn9QA@mail.gmail.com>
References: <17477-0af3c6ac6b0a6ae0@postgresql.org>
 <CAD21AoCF5EWSXUR6MOGUWeqqo5bGw=_4LHDbwhPjO4x+xQn9QA@mail.gmail.com>
Comments: In-reply-to Masahiko Sawada <sawada.mshk@gmail.com>
	message dated "Mon, 09 May 2022 23:03:56 +0900"
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Date: Mon, 09 May 2022 11:25:38 -0400
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Masahiko Sawada <sawada.mshk@gmail.com> writes:
> It seems like transformValuesClause() cannot handle properly the value
> clause having a relation that has an empty column. Should we raise an
> error in this case?

Given that we try to support zero-column relations, I'm not sure why
we'd insist on disallowing zero-column VALUES.  I think the problem
is that the code in transformValuesClause needs to be tweaked to
make that work.  The attached quick hack seems to do the trick.

			regards, tom lane


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diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 0144284aa3..6b54e8e46d 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -1424,7 +1424,7 @@ static Query *
 transformValuesClause(ParseState *pstate, SelectStmt *stmt)
 {
 	Query	   *qry =3D makeNode(Query);
-	List	   *exprsLists;
+	List	   *exprsLists =3D NIL;
 	List	   *coltypes =3D NIL;
 	List	   *coltypmods =3D NIL;
 	List	   *colcollations =3D NIL;
@@ -1508,6 +1508,9 @@ transformValuesClause(ParseState *pstate, SelectStmt=
 *stmt)
 =

 		/* Release sub-list's cells to save memory */
 		list_free(sublist);
+
+		/* Prepare an exprsLists element for this row */
+		exprsLists =3D lappend(exprsLists, NIL);
 	}
 =

 	/*
@@ -1551,17 +1554,7 @@ transformValuesClause(ParseState *pstate, SelectStm=
t *stmt)
 	/*
 	 * Finally, rearrange the coerced expressions into row-organized lists.
 	 */
-	exprsLists =3D NIL;
-	foreach(lc, colexprs[0])
-	{
-		Node	   *col =3D (Node *) lfirst(lc);
-		List	   *sublist;
-
-		sublist =3D list_make1(col);
-		exprsLists =3D lappend(exprsLists, sublist);
-	}
-	list_free(colexprs[0]);
-	for (i =3D 1; i < sublist_length; i++)
+	for (i =3D 0; i < sublist_length; i++)
 	{
 		forboth(lc, colexprs[i], lc2, exprsLists)
 		{
@@ -1569,6 +1562,7 @@ transformValuesClause(ParseState *pstate, SelectStmt=
 *stmt)
 			List	   *sublist =3D lfirst(lc2);
 =

 			sublist =3D lappend(sublist, col);
+			lfirst(lc2) =3D sublist;
 		}
 		list_free(colexprs[i]);
 	}

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