To: mailreg@numerixtechnology.de, pgsql-patches@postgresql.org
Cc: Greg Stark <gsstark@mit.edu>
Subject: Re: [SQL] COUNT(*) to find records which have a certain number of
	dependencies ?
References: <414EF3E6.9040202@numerixtechnology.de>
	<87llf4hjv2.fsf@stark.xeocode.com>
	<414F348A.2020608@numerixtechnology.de>
	<877jqohdoj.fsf@stark.xeocode.com>
	<414F43A8.8000101@numerixtechnology.de>
In-Reply-To: <414F43A8.8000101@numerixtechnology.de>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 20 Sep 2004 17:39:40 -0400
Message-ID: <87y8j4fwmb.fsf@stark.xeocode.com>
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T E Schmitz <mailreg@numerixtechnology.de> writes:

> There's a German saying "Go and find a parking-meter", i.e. suggesting to pop a
> coin in the parking-meter and talk to it as nobody else wants to listen. ;-)

Yes well I anticipated such a response. So I tried my hand at it myself.

Well I finally found a problem tractable enough for me to get all the way from
start to end in a single sitting. Here's a simple solution to my complaint.

This patch allows subqueries without aliases. This is SQL-non-spec-compliant
syntax that Oracle supports and many users expect to work. It's also just
damned convenient, especially for simple ad-hoc queries. 

There was a comment saying an alias name would have to be constructed so I
took that approach. It seems like it would have been cleaner to just ensure
that the code doesn't fail when no alias is present. But I have no idea how
much work would be involved in that, so I just took advice from the anonymous
author of the comment.

Incidentally, It seems weird to me that the counter doesn't reset for every
query. Perhaps I should change that?


Index: src/backend/parser/gram.y
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/parser/gram.y,v
retrieving revision 2.475
diff -u -p -c -r2.475 gram.y
cvs diff: conflicting specifications of output style
*** src/backend/parser/gram.y	29 Aug 2004 04:12:35 -0000	2.475
--- src/backend/parser/gram.y	20 Sep 2004 21:34:13 -0000
*************** table_ref:	relation_expr
*** 5158,5177 ****
  				{
  					/*
  					 * The SQL spec does not permit a subselect
! 					 * (<derived_table>) without an alias clause,
! 					 * so we don't either.  This avoids the problem
! 					 * of needing to invent a unique refname for it.
! 					 * That could be surmounted if there's sufficient
! 					 * popular demand, but for now let's just implement
! 					 * the spec and see if anyone complains.
! 					 * However, it does seem like a good idea to emit
! 					 * an error message that's better than "syntax error".
  					 */
! 					ereport(ERROR,
! 							(errcode(ERRCODE_SYNTAX_ERROR),
! 							 errmsg("subquery in FROM must have an alias"),
! 							 errhint("For example, FROM (SELECT ...) [AS] foo.")));
! 					$$ = NULL;
  				}
  			| select_with_parens alias_clause
  				{
--- 5158,5172 ----
  				{
  					/*
  					 * The SQL spec does not permit a subselect
! 					 * (<derived_table>) without an alias clause, We surmount
! 					 * this because of popular demand by gining up a fake name
! 					 * in transformRangeSubselect
  					 */
! 
! 					RangeSubselect *n = makeNode(RangeSubselect);
! 					n->subquery = $1;
! 					n->alias = NULL;
! 					$$ = (Node *) n;
  				}
  			| select_with_parens alias_clause
  				{
Index: src/backend/parser/parse_clause.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/parser/parse_clause.c,v
retrieving revision 1.136
diff -u -p -c -r1.136 parse_clause.c
cvs diff: conflicting specifications of output style
*** src/backend/parser/parse_clause.c	29 Aug 2004 05:06:44 -0000	1.136
--- src/backend/parser/parse_clause.c	20 Sep 2004 21:34:14 -0000
*************** transformRangeSubselect(ParseState *psta
*** 418,426 ****
  	 * an unlabeled subselect.
  	 */
  	if (r->alias == NULL)
! 		ereport(ERROR,
! 				(errcode(ERRCODE_SYNTAX_ERROR),
! 				 errmsg("subquery in FROM must have an alias")));
  
  	/*
  	 * Analyze and transform the subquery.
--- 418,434 ----
  	 * an unlabeled subselect.
  	 */
  	if (r->alias == NULL)
! 	{
! 		static int subquery_counter = 1;
! 		static char buf[30];
! 
! 		sprintf(buf, "*SUBQUERY*%d*", subquery_counter++);
! 
! 		r->alias = makeNode(Alias);
! 		r->alias->aliasname = pstrdup(buf);
! 		r->alias->colnames = NULL;
! 	}
! 	
  
  	/*
  	 * Analyze and transform the subquery.