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Modify the definition of window-function PARTITION BY and ORDER BY clauses

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so that their elements are always taken as simple expressions over the
query's input columns.  It originally seemed like a good idea to make them
act exactly like GROUP BY and ORDER BY, right down to the SQL92-era behavior
of accepting output column names or numbers.  However, that was not such a
great idea, for two reasons:

1. It permits circular references, as exhibited in bug #5018: the output
column could be the one containing the window function itself.  (We actually
had a regression test case illustrating this, but nobody thought twice about
how confusing that would be.)

2. It doesn't seem like a good idea for, eg, "lead(foo) OVER (ORDER BY foo)"
to potentially use two completely different meanings for "foo".

Accordingly, narrow down the behavior of window clauses to use only the
SQL99-compliant interpretation that the expressions are simple expressions.
This commit is contained in:
Tom Lane
2009-08-27 20:08:03 +00:00
parent f065b17d9f
commit bb16dc49ab
7 changed files with 116 additions and 63 deletions
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13
src/backend/parser/analyze.c
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@ -17,7 +17,7 @@
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/parser/analyze.c,v 1.389 2009/06/11 14:48:59 momjian Exp $
* $PostgreSQL: pgsql/src/backend/parser/analyze.c,v 1.390 2009/08/27 20:08:02 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -825,13 +825,14 @@ transformSelectStmt(ParseState *pstate, SelectStmt *stmt)
qry->sortClause = transformSortClause(pstate,
stmt->sortClause,
&qry->targetList,
true /* fix unknowns */ );
true /* fix unknowns */,
false /* not window function */);
qry->groupClause = transformGroupClause(pstate,
stmt->groupClause,
&qry->targetList,
qry->sortClause,
false);
false /* not window function */);
if (stmt->distinctClause == NIL)
{
@ -1039,7 +1040,8 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
qry->sortClause = transformSortClause(pstate,
stmt->sortClause,
&qry->targetList,
true /* fix unknowns */ );
true /* fix unknowns */,
false /* not window function */);
qry->limitOffset = transformLimitClause(pstate, stmt->limitOffset,
"OFFSET");
@ -1291,7 +1293,8 @@ transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt)
qry->sortClause = transformSortClause(pstate,
sortClause,
&qry->targetList,
false /* no unknowns expected */ );
false /* no unknowns expected */,
false /* not window function */);
pstate->p_rtable = list_truncate(pstate->p_rtable, sv_rtable_length);
pstate->p_relnamespace = sv_relnamespace;