Fix grammar for subscripting or field selection from a sub-SELECT result.

Such cases should work, but the grammar failed to accept them because of
our ancient precedence hacks to convince bison that extra parentheses
around a sub-SELECT in an expression are unambiguous.  (Formally, they
*are* ambiguous, but we don't especially care whether they're treated as
part of the sub-SELECT or part of the expression.  Bison cares, though.)
Fix by adding a redundant-looking production for this case.

This is a fine example of why fixing shift/reduce conflicts via
precedence declarations is more dangerous than it looks: you can easily
cause the parser to reject cases that should work.

This has been wrong since commit 3db4056e22b0c6b2adc92543baf8408d2894fe91
or maybe before, and apparently some people have been working around it
by inserting no-op casts.  That method introduces a dump/reload hazard,
as illustrated in bug #7838 from Jan Mate.  Hence, back-patch to all
active branches.

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index eb75f37e47c5aac8bc69c43302b9a4d925a9720e..3343c9692c958fdfcaffbd55569f2adb2b0ec889 100644 (file)
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -7786,6 +7786,28 @@ c_expr:          columnref                                                               { $$ = $1; }
                                        n->subselect = $1;
                                        $$ = (Node *)n;
                                }
+                       | select_with_parens indirection
+                               {
+                                       /*
+                                        * Because the select_with_parens nonterminal is designed
+                                        * to "eat" as many levels of parens as possible, the
+                                        * '(' a_expr ')' opt_indirection production above will
+                                        * fail to match a sub-SELECT with indirection decoration;
+                                        * the sub-SELECT won't be regarded as an a_expr as long
+                                        * as there are parens around it.  To support applying
+                                        * subscripting or field selection to a sub-SELECT result,
+                                        * we need this redundant-looking production.
+                                        */
+                                       SubLink *n = makeNode(SubLink);
+                                       A_Indirection *a = makeNode(A_Indirection);
+                                       n->subLinkType = EXPR_SUBLINK;
+                                       n->testexpr = NULL;
+                                       n->operName = NIL;
+                                       n->subselect = $1;
+                                       a->arg = (Node *)n;
+                                       a->indirection = $2;
+                                       $$ = (Node *)a;
+                               }
                        | EXISTS select_with_parens
                                {
                                        SubLink *n = makeNode(SubLink);

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index 00f931b6df0659cbda319d15884f2c5427ba3eab..82d4b3849398a07326f627f7a5440b0cb5744023 100644 (file)
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -17,6 +17,61 @@ SELECT 1 AS zero WHERE 1 IN (SELECT 2);
 ------
 (0 rows)
 
+-- Check grammar's handling of extra parens in assorted contexts
+SELECT * FROM (SELECT 1 AS x) ss;
+ x 
+---
+ 1
+(1 row)
+
+SELECT * FROM ((SELECT 1 AS x)) ss;
+ x 
+---
+ 1
+(1 row)
+
+(SELECT 2) UNION SELECT 2;
+ ?column? 
+----------
+        2
+(1 row)
+
+((SELECT 2)) UNION SELECT 2;
+ ?column? 
+----------
+        2
+(1 row)
+
+SELECT ((SELECT 2) UNION SELECT 2);
+ ?column? 
+----------
+        2
+(1 row)
+
+SELECT (((SELECT 2)) UNION SELECT 2);
+ ?column? 
+----------
+        2
+(1 row)
+
+SELECT (SELECT ARRAY[1,2,3])[1];
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT ((SELECT ARRAY[1,2,3]))[2];
+ ?column? 
+----------
+        2
+(1 row)
+
+SELECT (((SELECT ARRAY[1,2,3])))[3];
+ ?column? 
+----------
+        3
+(1 row)
+
 -- Set up some simple test tables
 CREATE TABLE SUBSELECT_TBL (
   f1 integer,

diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index ac98d34c7900177072d7fa19caf1359d8be0527f..41eb230c3450f6329ad11b671aa4379f244fb6fb 100644 (file)
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -8,6 +8,21 @@ SELECT 1 AS zero WHERE 1 NOT IN (SELECT 1);
 
 SELECT 1 AS zero WHERE 1 IN (SELECT 2);
 
+-- Check grammar's handling of extra parens in assorted contexts
+
+SELECT * FROM (SELECT 1 AS x) ss;
+SELECT * FROM ((SELECT 1 AS x)) ss;
+
+(SELECT 2) UNION SELECT 2;
+((SELECT 2)) UNION SELECT 2;
+
+SELECT ((SELECT 2) UNION SELECT 2);
+SELECT (((SELECT 2)) UNION SELECT 2);
+
+SELECT (SELECT ARRAY[1,2,3])[1];
+SELECT ((SELECT ARRAY[1,2,3]))[2];
+SELECT (((SELECT ARRAY[1,2,3])))[3];
+
 -- Set up some simple test tables
 
 CREATE TABLE SUBSELECT_TBL (