database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-03 20:02:46 +03:00
Code Activity

Support multi-argument UNNEST(), and TABLE() syntax for multiple functions.

Browse Source 
This patch adds the ability to write TABLE( function1(), function2(), ...)
as a single FROM-clause entry.  The result is the concatenation of the
first row from each function, followed by the second row from each
function, etc; with NULLs inserted if any function produces fewer rows than
others.  This is believed to be a much more useful behavior than what
Postgres currently does with multiple SRFs in a SELECT list.

This syntax also provides a reasonable way to combine use of column
definition lists with WITH ORDINALITY: put the column definition list
inside TABLE(), where it's clear that it doesn't control the ordinality
column as well.

Also implement SQL-compliant multiple-argument UNNEST(), by turning
UNNEST(a,b,c) into TABLE(unnest(a), unnest(b), unnest(c)).

The SQL standard specifies TABLE() with only a single function, not
multiple functions, and it seems to require an implicit UNNEST() which is
not what this patch does.  There may be something wrong with that reading
of the spec, though, because if it's right then the spec's TABLE() is just
a pointless alternative spelling of UNNEST().  After further review of
that, we might choose to adopt a different syntax for what this patch does,
but in any case this functionality seems clearly worthwhile.

Andrew Gierth, reviewed by Zoltán Böszörményi and Heikki Linnakangas, and
significantly revised by me
This commit is contained in:
Tom Lane
2013-11-21 19:37:02 -05:00
parent 38f4328981
commit 784e762e88
48 changed files with 2643 additions and 1207 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
src/backend/optimizer/path/allpaths.c
View File

@ -18,6 +18,7 @@
#include <math.h>
#include "catalog/pg_class.h"
#include "catalog/pg_operator.h"
#include "foreign/fdwapi.h"
#include "nodes/nodeFuncs.h"
#ifdef OPTIMIZER_DEBUG
@ -1258,6 +1259,7 @@ static void
set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
Relids required_outer;
List *pathkeys = NIL;
/*
* We don't support pushing join clauses into the quals of a function
@ -1266,8 +1268,55 @@ set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
*/
required_outer = rel->lateral_relids;
/*
* The result is considered unordered unless ORDINALITY was used, in which
* case it is ordered by the ordinal column (the last one). See if we
* care, by checking for uses of that Var in equivalence classes.
*/
if (rte->funcordinality)
{
AttrNumber ordattno = rel->max_attr;
Var *var = NULL;
ListCell *lc;
/*
* Is there a Var for it in reltargetlist? If not, the query did not
* reference the ordinality column, or at least not in any way that
* would be interesting for sorting.
*/
foreach(lc, rel->reltargetlist)
{
Var *node = (Var *) lfirst(lc);
/* checking varno/varlevelsup is just paranoia */
if (IsA(node, Var) &&
node->varattno == ordattno &&
node->varno == rel->relid &&
node->varlevelsup == 0)
{
var = node;
break;
}
}
/*
* Try to build pathkeys for this Var with int8 sorting. We tell
* build_expression_pathkey not to build any new equivalence class; if
* the Var isn't already mentioned in some EC, it means that nothing
* cares about the ordering.
*/
if (var)
pathkeys = build_expression_pathkey(root,
(Expr *) var,
NULL, /* below outer joins */
Int8LessOperator,
rel->relids,
false);
}
/* Generate appropriate path */
add_path(rel, create_functionscan_path(root, rel, required_outer));
add_path(rel, create_functionscan_path(root, rel,
pathkeys, required_outer));
/* Select cheapest path (pretty easy in this case...) */
set_cheapest(rel);