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Further fix dumping of views that contain just VALUES(...).
It turns out that commit e9f1c01 missed a case: we must print a VALUES clause in long format if get_query_def is given a resultDesc that would require the query's output column name(s) to be different from what the bare VALUES clause would produce. This applies in case an ALTER ... RENAME COLUMN has been done to a view that formerly could be printed in simple format, as shown in the added regression test case. It also explains bug #16119 from Dmitry Telpt, because it turns out that (unlike CREATE VIEW) CREATE MATERIALIZED VIEW fails to apply any column aliases it's given to the stored ON SELECT rule. So to get them to be printed, we have to account for the resultDesc renaming. It might be worth changing the matview code so that it creates the ON SELECT rule with the correct aliases; but we'd still need these messy checks in get_simple_values_rte to handle the case of a subsequent column rename, so any such change would be just neatnik-ism not a bug fix. Like the previous patch, back-patch to all supported branches. Discussion: https://postgr.es/m/16119-e64823f30a45a754@postgresql.org
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‎src/backend/utils/adt/ruleutils.c

Lines changed: 24 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -5374,19 +5374,20 @@ get_select_query_def(Query *query, deparse_context *context,
53745374
}
53755375

53765376
/*
5377-
* Detect whether query looks like SELECT ... FROM VALUES();
5378-
* if so, return the VALUES RTE. Otherwise return NULL.
5377+
* Detect whether query looks like SELECT ... FROM VALUES(),
5378+
* with no need to rename the output columns of the VALUES RTE.
5379+
* If so, return the VALUES RTE. Otherwise return NULL.
53795380
*/
53805381
static RangeTblEntry *
5381-
get_simple_values_rte(Query *query)
5382+
get_simple_values_rte(Query *query, TupleDesc resultDesc)
53825383
{
53835384
RangeTblEntry *result = NULL;
53845385
ListCell *lc;
53855386

53865387
/*
5387-
* We want to return true even if the Query also contains OLD or NEW rule
5388-
* RTEs. So the idea is to scan the rtable and see if there is only one
5389-
* inFromCl RTE that is a VALUES RTE.
5388+
* We want to detect a match even if the Query also contains OLD or NEW
5389+
* rule RTEs. So the idea is to scan the rtable and see if there is only
5390+
* one inFromCl RTE that is a VALUES RTE.
53905391
*/
53915392
foreach(lc, query->rtable)
53925393
{
@@ -5409,23 +5410,36 @@ get_simple_values_rte(Query *query)
54095410
* parser/analyze.c will never generate a "bare" VALUES RTE --- they only
54105411
* appear inside auto-generated sub-queries with very restricted
54115412
* structure. However, DefineView might have modified the tlist by
5412-
* injecting new column aliases; so compare tlist resnames against the
5413-
* RTE's names to detect that.
5413+
* injecting new column aliases, or we might have some other column
5414+
* aliases forced by a resultDesc. We can only simplify if the RTE's
5415+
* column names match the names that get_target_list() would select.
54145416
*/
54155417
if (result)
54165418
{
54175419
ListCell *lcn;
5420+
int colno;
54185421

54195422
if (list_length(query->targetList) != list_length(result->eref->colnames))
54205423
return NULL; /* this probably cannot happen */
5424+
colno = 0;
54215425
forboth(lc, query->targetList, lcn, result->eref->colnames)
54225426
{
54235427
TargetEntry *tle = (TargetEntry *) lfirst(lc);
54245428
char *cname = strVal(lfirst(lcn));
5429+
char *colname;
54255430

54265431
if (tle->resjunk)
54275432
return NULL; /* this probably cannot happen */
5428-
if (tle->resname == NULL || strcmp(tle->resname, cname) != 0)
5433+
5434+
/* compute name that get_target_list would use for column */
5435+
colno++;
5436+
if (resultDesc && colno <= resultDesc->natts)
5437+
colname = NameStr(TupleDescAttr(resultDesc, colno - 1)->attname);
5438+
else
5439+
colname = tle->resname;
5440+
5441+
/* does it match the VALUES RTE? */
5442+
if (colname == NULL || strcmp(colname, cname) != 0)
54295443
return NULL; /* column name has been changed */
54305444
}
54315445
}
@@ -5453,7 +5467,7 @@ get_basic_select_query(Query *query, deparse_context *context,
54535467
* VALUES part. This reverses what transformValuesClause() did at parse
54545468
* time.
54555469
*/
5456-
values_rte = get_simple_values_rte(query);
5470+
values_rte = get_simple_values_rte(query, resultDesc);
54575471
if (values_rte)
54585472
{
54595473
get_values_def(values_rte->values_lists, context);

‎src/test/regress/expected/rules.out

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3023,6 +3023,18 @@ create view rule_v1 as values(1,2);
30233023
View definition:
30243024
VALUES (1,2);
30253025

3026+
alter table rule_v1 rename column column2 to q2;
3027+
\d+ rule_v1
3028+
View "public.rule_v1"
3029+
Column | Type | Collation | Nullable | Default | Storage | Description
3030+
---------+---------+-----------+----------+---------+---------+-------------
3031+
column1 | integer | | | | plain |
3032+
q2 | integer | | | | plain |
3033+
View definition:
3034+
SELECT "*VALUES*".column1,
3035+
"*VALUES*".column2 AS q2
3036+
FROM (VALUES (1,2)) "*VALUES*";
3037+
30263038
drop view rule_v1;
30273039
create view rule_v1(x) as values(1,2);
30283040
\d+ rule_v1

‎src/test/regress/sql/rules.sql

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1047,6 +1047,8 @@ DROP TABLE rule_t1;
10471047
--
10481048
create view rule_v1 as values(1,2);
10491049
\d+ rule_v1
1050+
alter table rule_v1 rename column column2 to q2;
1051+
\d+ rule_v1
10501052
drop view rule_v1;
10511053
create view rule_v1(x) as values(1,2);
10521054
\d+ rule_v1

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