Evgen Potemkin kirjutas R, 22.11.2002 kell 15:57:
> Hi there!
>
> Patch is posted to pgsql-patches. docs inside.
It would of course be nice to support both Oracle and ISO/ANSI syntaxes,
but I'm afraid that the (+) may clash with our overloadable operators
feature.
> SQL 99 version will be later.
I attach a railroad diagram of SQL99 "WITH RECURSIVE" and a diff against
mid-summer gram.y which implements half of SQL99 _syntax_ (just the WITH
{RECURSIVE} part, SEARCH (tree search order order) and CYCLE (recursion
control) clauses are missing).
WITH clause seems to be quite useful in its own right as well, not just
for recursive queries, so I guess that someone with good knwledge of
postgresql internals could get plain WITH working quite fast -
The main difference between subqueries defined in WITH clause and in
FROM clause is that while subqueries in FROM don't see each other in
their namespaces, the ones in WITH either see all preceeding ones (plain
with) or just all in WITH clause (WITH RECURSIVE)
--
Hannu
<>276a277,285
>
> /* WITH CLAUSE */
>
> %typeopt_recursive
> %type with_list_element
> %type with_list
>
> /* /WITH CLAUSE */
>
374c383,387
< READ, REAL, REFERENCES, REINDEX, RELATIVE, RENAME, REPLACE,
---
> READ, REAL,
>
> RECURSIVE,
>
> REFERENCES, REINDEX, RELATIVE, RENAME, REPLACE,
4023,4024c4036,4037
< SelectStmt: select_no_parens %prec UMINUS
< | select_with_parens%prec UMINUS
---
> SelectStmt: select_no_parens%prec UMINUS
> | select_with_parens%prec UMINUS
4028,4029c4041,4042
< '(' select_no_parens ')'{ $$ =
$2; }
< | '(' select_with_parens ')'{ $$ = $2; }
---
> '(' select_no_parens ')'
> { $$ = $2; }
> | '(' select_with_parens ')'
> { $$ = $2; }
4031a4045
>
4033c4047,4058
< simple_select { $$ =
$1; }
---
> simple_select
> { $$ = $1; }
> | WITH opt_recursive with_list simple_select
> {
> /* this should actually blend in subselects
>from WITH
>* just replacing will do the WRONG THING
>*/
> ((SelectStmt *) $4 )->with_recursive = $2;
> ((SelectStmt *) $4 )->withClause = $3;
>
> $$ = $4;
> }
>
4039a4065,4072
> /*
> | WITH RECURSIVE with_list select_clause sort_clause
>opt_for_update_clause opt_select_limit
> {
> insertSelectOptions((SelectStmt *) $2, $3, $4,
> nth(0,
>$5), nth(1, $5));
> $$ = $1;
> }
> */
4045a4079,4087
> /*
> | WITH RECURSIVE with_list select_clause for_update_clause
>opt_select_limit
> {
> insertSelectOptions((SelectStmt *) $2, NIL, $3,
> nth(0,
>$4), nth(1, $4));
> $$ = $1;
> }
> */
>
4051a4094,4100
> | WITH opt_recursive with_list select_clause select_limit
> {
> insertSelectOptions((SelectStmt *) $4, NIL,
>NIL,
> nth(0,
>$5), nth(1, $5));
> $$ = $4;
> }
>
4053a4103,4141
> /* WITH CLAUSE
> *
> * ANSI/ISO SQL99 p 7.13-7.14
> *
> */
>
> opt_recursive:
> RECURSIVE { $$ = TRUE; }
> | /*EMPTY */{ $$ = FALSE; }
> ;
>
> with_list:
> with_list_element { $$ =
>makeList1($1); }
> | with_list ',' with_list_element { $$ = lappend($1, $3); }
> ;
>
> with_list_element:
> ColId '(' name_list ')' AS select_with_parens
> {
> RangeSubselect *n = makeNode(RangeSubselect);
> n->subquery = $6;
>
