This was discussed previously in [1], and there seemed to be general
consensus in favour of it, but no new patch emerged.
Attached is a patch that takes the approach of not generating an alias
at all, which seems to be neater and simpler, and less code than
trying to generate a unique alias.
It still generates an eref for the subquery RTE, which has a made-up
relation name, but that is marked as not visible on the
ParseNamespaceItem, so it doesn't conflict with anything else, need
not be unique, and cannot be used for qualified references to the
subquery's columns.
The only place that exposes the eref's made-up relation name is the
existing query deparsing code in ruleutils.c, which uniquifies it and
generates SQL spec-compliant output. For example:
CREATE OR REPLACE VIEW test_view AS
SELECT *
FROM (SELECT a, b FROM foo),
(SELECT c, d FROM bar)
WHERE a = c;
\sv test_view
CREATE OR REPLACE VIEW public.test_view AS
SELECT subquery.a,
subquery.b,
subquery_1.c,
subquery_1.d
FROM ( SELECT foo.a,
foo.b
FROM foo) subquery,
( SELECT bar.c,
bar.d
FROM bar) subquery_1
WHERE subquery.a = subquery_1.c
Regards,
Dean
[1]
https://www.postgresql.org/message-id/flat/1487773980.3143.15.camel%40oopsware.de
diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
new file mode 100644
index 80bb8ad..8cae456
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -51,7 +51,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replacea
[ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ] [ [ AS ] <replaceable class="parameter">alias</replaceable> [ ( <replaceable class="parameter">column_alias</replaceable> [, ...] ) ] ]
[ TABLESAMPLE <replaceable class="parameter">sampling_method</replaceable> ( <replaceable class="parameter">argument</replaceable> [, ...] ) [ REPEATABLE ( <replaceable class="parameter">seed</replaceable> ) ] ]
- [ LATERAL ] ( <replaceable class="parameter">select</replaceable> ) [ AS ] <replaceable class="parameter">alias</replaceable> [ ( <replaceable class="parameter">column_alias</replaceable> [, ...] ) ]
+ [ LATERAL ] ( <replaceable class="parameter">select</replaceable> ) [ [ AS ] <replaceable class="parameter">alias</replaceable> [ ( <replaceable class="parameter">column_alias</replaceable> [, ...] ) ] ]
<replaceable class="parameter">with_query_name</replaceable> [ [ AS ] <replaceable class="parameter">alias</replaceable> [ ( <replaceable class="parameter">column_alias</replaceable> [, ...] ) ] ]
[ LATERAL ] <replaceable class="parameter">function_name</replaceable> ( [ <replaceable class="parameter">argument</replaceable> [, ...] ] )
[ WITH ORDINALITY ] [ [ AS ] <replaceable class="parameter">alias</replaceable> [ ( <replaceable class="parameter">column_alias</replaceable> [, ...] ) ] ]
@@ -490,11 +490,18 @@ TABLE [ ONLY ] <replaceable class="param
output were created as a temporary table for the duration of
this single <command>SELECT</command> command. Note that the
sub-<command>SELECT</command> must be surrounded by
- parentheses, and an alias <emphasis>must</emphasis> be
- provided for it. A
+ parentheses. A
<link linkend="sql-values"><command>VALUES</command></link> command
can also be used here.
</para>
+
+ <para>
+ An alias may be provided to name the output of the
+ sub-<command>SELECT</command>, and optionally rename its columns.
+ Note that according to the SQL standard, a
+ sub-<command>SELECT</command> <emphasis>must</emphasis> have an alias,
+ whereas in <productname>PostgreSQL</productname> it is optional.
+ </para>
</listitem>
</varlistentry>
@@ -2041,6 +2048,16 @@ SELECT 2+2;
</para>
</refsect2>
+ <refsect2>
+ <title>Omitting sub-<command>SELECT</command> aliases in <literal>FROM</literal></title>
+
+ <para>
+ According to the SQL standard, a sub-<command>SELECT</command> in the
+ <literal>FROM</literal> list must have an alias. In
+ <productname>PostgreSQL</productname>, this alias may be omitted.
+ </para>
+ </refsect2>
+
<refsect2>
<title><literal>ONLY</literal> and Inheritance</title>
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 969c9c1..3b25f7c
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -13346,33 +13346,6 @@ table_ref: relation_expr opt_alias_claus
n->lateral = false;
n->subquery = $1;
n->alias = $2;
- /*
- * 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".
- */
- if ($2 == NULL)
- {
- if (IsA($1, SelectStmt) &&
- ((SelectStmt *) $1)->valuesLists)
- ereport(ERROR,
- (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("VALUES in FROM must have an alias"),
- errhint("For example, FROM (VALUES ...) [AS] foo."),
- parser_errposition(@1)));
- else
- ereport(ERROR,
- (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("subquery in FROM must have an alias"),
- errhint("For example, FROM (SELECT ...) [AS] foo."),
- parser_errposition(@1)));
- }
$$ = (Node *) n;
}
| LATERAL_P select_with_parens opt_alias_clause
@@ -13382,23 +13355,6 @@ table_ref: relation_expr opt_alias_claus
n->lateral = true;
n->subquery = $2;
n->alias = $3;
- /* same comment as above */
- if ($3 == NULL)
- {
- if (IsA($2, SelectStmt) &&
- ((SelectStmt *) $2)->valuesLists)
- ereport(ERROR,
- (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("VALUES in FROM must have an alias"),
- errhint("For example, FROM (VALUES ...) [AS] foo."),
- parser_errposition(@2)));
- else
- ereport(ERROR,
- (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("subquery in FROM must have an alias"),
- errhint("For example, FROM (SELECT ...) [AS] foo."),
- parser_errposition(@2)));
- }
$$ = (Node *) n;
}
| joined_table
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
new file mode 100644
index c655d18..5a18107
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -404,16 +404,6 @@ transformRangeSubselect(ParseState *psta
Query *query;
/*
- * We require user to supply an alias for a subselect, per SQL92. To relax
- * this, we'd have to be prepared to gin up a unique alias for an
- * unlabeled subselect. (This is just elog, not ereport, because the
- * grammar should have enforced it already. It'd probably be better to
- * report the error here, but we don't have a good error location here.)
- */
- if (r->alias == NULL)
- elog(ERROR, "subquery in FROM must have an alias");
-
- /*
* Set p_expr_kind to show this parse level is recursing to a subselect.
* We can't be nested within any expression, so don't need save-restore
* logic here.
@@ -430,10 +420,14 @@ transformRangeSubselect(ParseState *psta
pstate->p_lateral_active = r->lateral;
/*
- * Analyze and transform the subquery.
+ * Analyze and transform the subquery. Note that if the subquery doesn't
+ * have an alias, it can't be explicitly selected for locking, but locking
+ * might still be required (if there is an all-tables locking clause).
*/
query = parse_sub_analyze(r->subquery, pstate, NULL,
- isLockedRefname(pstate, r->alias->aliasname),
+ isLockedRefname(pstate,
+ r->alias == NULL ? NULL :
+ r->alias->aliasname),
true);
/* Restore state */
diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
new file mode 100644
index 926dcbf..68ff2cc
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -1577,7 +1577,11 @@ addRangeTableEntryForRelation(ParseState
* Then, construct and return a ParseNamespaceItem for the new RTE.
*
* This is much like addRangeTableEntry() except that it makes a subquery RTE.
- * Note that an alias clause *must* be supplied.
+ *
+ * If the subquery does not have an alias, the auto-generated relation name in
+ * the returned ParseNamespaceItem will be marked as not visible, and so only
+ * unqualified references to the subquery columns will be allowed, and the
+ * relation name will not conflict with others in the pstate's namespace list.
*/
ParseNamespaceItem *
addRangeTableEntryForSubquery(ParseState *pstate,
@@ -1587,7 +1591,6 @@ addRangeTableEntryForSubquery(ParseState
bool inFromCl)
{
RangeTblEntry *rte = makeNode(RangeTblEntry);
- char *refname = alias->aliasname;
Alias *eref;
int numaliases;
List *coltypes,
@@ -1595,6 +1598,7 @@ addRangeTableEntryForSubquery(ParseState
*colcollations;
int varattno;
ListCell *tlistitem;
+ ParseNamespaceItem *nsitem;
Assert(pstate != NULL);
@@ -1602,7 +1606,7 @@ addRangeTableEntryForSubquery(ParseState
rte->subquery = subquery;
rte->alias = alias;
- eref = copyObject(alias);
+ eref = alias ? copyObject(alias) : makeAlias("subquery", NIL);
numaliases = list_length(eref->colnames);
/* fill in any unspecified alias columns, and extract column type info */
@@ -1634,7 +1638,7 @@ addRangeTableEntryForSubquery(ParseState
ereport(ERROR,
(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
errmsg("table \"%s\" has %d columns available but %d columns specified",
- refname, varattno, numaliases)));
+ eref->aliasname, varattno, numaliases)));
rte->eref = eref;
@@ -1665,8 +1669,15 @@ addRangeTableEntryForSubquery(ParseState
* Build a ParseNamespaceItem, but don't add it to the pstate's namespace
* list --- caller must do that if appropriate.
*/
- return buildNSItemFromLists(rte, list_length(pstate->p_rtable),
- coltypes, coltypmods, colcollations);
+ nsitem = buildNSItemFromLists(rte, list_length(pstate->p_rtable),
+ coltypes, coltypmods, colcollations);
+
+ /*
+ * Mark it visible as a relation name only if it had a user-written alias.
+ */
+ nsitem->p_rel_visible = (alias != NULL);
+
+ return nsitem;
}
/*
@@ -2520,6 +2531,10 @@ addRangeTableEntryForENR(ParseState *pst
* This is used when we have not yet done transformLockingClause, but need
* to know the correct lock to take during initial opening of relations.
*
+ * Note that refname may be NULL (for a subquery without an alias), in which
+ * case the relation can't be locked by name, but it might still be locked if
+ * a locking clause requests that all tables be locked.
+ *
* Note: we pay no attention to whether it's FOR UPDATE vs FOR SHARE,
* since the table-level lock is the same either way.
*/
@@ -2544,7 +2559,7 @@ isLockedRefname(ParseState *pstate, cons
/* all tables used in query */
return true;
}
- else
+ else if (refname != NULL)
{
/* just the named tables */
ListCell *l2;
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index c3937a6..9d285fe
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -11728,7 +11728,11 @@ get_from_clause_item(Node *jtnode, Query
else if (rte->rtekind == RTE_SUBQUERY ||
rte->rtekind == RTE_VALUES)
{
- /* Alias is syntactically required for SUBQUERY and VALUES */
+ /*
+ * For a subquery, always print alias. This makes the output SQL
+ * spec-compliant, even though we allow the alias to be omitted on
+ * input.
+ */
printalias = true;
}
else if (rte->rtekind == RTE_CTE)
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
new file mode 100644
index cf9c759..962ebf6
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -246,8 +246,11 @@ struct ParseState
* visible for qualified references) but it does hide their columns
* (unqualified references to the columns refer to the JOIN, not the member
* tables, so we must not complain that such a reference is ambiguous).
- * Various special RTEs such as NEW/OLD for rules may also appear with only
- * one flag set.
+ * Conversely, a subquery without an alias does not hide the columns selected
+ * by the subquery, but it does hide the auto-generated relation name (so the
+ * subquery columns are visible for unqualified references only). Various
+ * special RTEs such as NEW/OLD for rules may also appear with only one flag
+ * set.
*
* While processing the FROM clause, namespace items may appear with
* p_lateral_only set, meaning they are visible only to LATERAL
diff --git a/src/interfaces/ecpg/preproc/ecpg.addons b/src/interfaces/ecpg/preproc/ecpg.addons
new file mode 100644
index 94f7d4a..e94da2a
--- a/src/interfaces/ecpg/preproc/ecpg.addons
+++ b/src/interfaces/ecpg/preproc/ecpg.addons
@@ -449,12 +449,6 @@ ECPG: into_clauseINTOOptTempTableName bl
$$= cat2_str(mm_strdup("into"), $2);
}
| ecpg_into { $$ = EMPTY; }
-ECPG: table_refselect_with_parensopt_alias_clause addon
- if ($2 == NULL)
- mmerror(PARSE_ERROR, ET_ERROR, "subquery in FROM must have an alias");
-ECPG: table_refLATERAL_Pselect_with_parensopt_alias_clause addon
- if ($3 == NULL)
- mmerror(PARSE_ERROR, ET_ERROR, "subquery in FROM must have an alias");
ECPG: TypenameSimpleTypenameopt_array_bounds block
{ $$ = cat2_str($1, $2.str); }
ECPG: TypenameSETOFSimpleTypenameopt_array_bounds block
diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
new file mode 100644
index 45c75ee..f264a40
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -30,6 +30,12 @@ SELECT * FROM ((SELECT 1 AS x)) ss;
1
(1 row)
+SELECT * FROM ((SELECT 1 AS x)), ((SELECT * FROM ((SELECT 2 AS y))));
+ x | y
+---+---
+ 1 | 2
+(1 row)
+
(SELECT 2) UNION SELECT 2;
?column?
----------
@@ -196,6 +202,53 @@ SELECT f1 AS "Correlated Field"
3
(5 rows)
+-- Subselects without aliases
+SELECT count FROM (SELECT COUNT(DISTINCT name) FROM road);
+ count
+-------
+ 2911
+(1 row)
+
+SELECT COUNT(*) FROM (SELECT DISTINCT name FROM road);
+ count
+-------
+ 2911
+(1 row)
+
+SELECT * FROM (SELECT * FROM int4_tbl), (VALUES (123456)) WHERE f1 = column1;
+ f1 | column1
+--------+---------
+ 123456 | 123456
+(1 row)
+
+CREATE VIEW view_unnamed_ss AS
+SELECT * FROM (SELECT * FROM (SELECT abs(f1) AS a1 FROM int4_tbl)),
+ (SELECT * FROM int8_tbl)
+ WHERE a1 < 10 AND q1 > a1 ORDER BY q1, q2;
+SELECT * FROM view_unnamed_ss;
+ a1 | q1 | q2
+----+------------------+-------------------
+ 0 | 123 | 456
+ 0 | 123 | 4567890123456789
+ 0 | 4567890123456789 | -4567890123456789
+ 0 | 4567890123456789 | 123
+ 0 | 4567890123456789 | 4567890123456789
+(5 rows)
+
+\sv view_unnamed_ss
+CREATE OR REPLACE VIEW public.view_unnamed_ss AS
+ SELECT subquery.a1,
+ subquery_1.q1,
+ subquery_1.q2
+ FROM ( SELECT subquery_2.a1
+ FROM ( SELECT abs(int4_tbl.f1) AS a1
+ FROM int4_tbl) subquery_2) subquery,
+ ( SELECT int8_tbl.q1,
+ int8_tbl.q2
+ FROM int8_tbl) subquery_1
+ WHERE subquery.a1 < 10 AND subquery_1.q1 > subquery.a1
+ ORDER BY subquery_1.q1, subquery_1.q2
+DROP VIEW view_unnamed_ss;
--
-- Use some existing tables in the regression test
--
diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
new file mode 100644
index 94ba91f..e4b74a0
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -13,6 +13,8 @@ SELECT 1 AS zero WHERE 1 IN (SELECT 2);
SELECT * FROM (SELECT 1 AS x) ss;
SELECT * FROM ((SELECT 1 AS x)) ss;
+SELECT * FROM ((SELECT 1 AS x)), ((SELECT * FROM ((SELECT 2 AS y))));
+
(SELECT 2) UNION SELECT 2;
((SELECT 2)) UNION SELECT 2;
@@ -80,6 +82,24 @@ SELECT f1 AS "Correlated Field"
WHERE (f1, f2) IN (SELECT f2, CAST(f3 AS int4) FROM SUBSELECT_TBL
WHERE f3 IS NOT NULL);
+-- Subselects without aliases
+
+SELECT count FROM (SELECT COUNT(DISTINCT name) FROM road);
+SELECT COUNT(*) FROM (SELECT DISTINCT name FROM road);
+
+SELECT * FROM (SELECT * FROM int4_tbl), (VALUES (123456)) WHERE f1 = column1;
+
+CREATE VIEW view_unnamed_ss AS
+SELECT * FROM (SELECT * FROM (SELECT abs(f1) AS a1 FROM int4_tbl)),
+ (SELECT * FROM int8_tbl)
+ WHERE a1 < 10 AND q1 > a1 ORDER BY q1, q2;
+
+SELECT * FROM view_unnamed_ss;
+
+\sv view_unnamed_ss
+
+DROP VIEW view_unnamed_ss;
+
--
-- Use some existing tables in the regression test
--
