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 7a854e364d3dcbe4312cb8a90695647c1ab77c23..aead8ec224888513d648924b2354c8404351de87 100644 (file)
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -10634,6 +10634,29 @@ c_expr:                columnref                                                               { $$ = $1; }
                                        n->location = @1;
                                        $$ = (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;
+                                       n->location = @1;
+                                       a->arg = (Node *)n;
+                                       a->indirection = check_indirection($2, yyscanner);
+                                       $$ = (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 bc67a3e7ffeb2b5c3d68c3821ad7dd310cc6961f..400ebc318936d6040d8e775ecd0925740dbf5027 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];
+ array 
+-------
+     1
+(1 row)
+
+SELECT ((SELECT ARRAY[1,2,3]))[2];
+ array 
+-------
+     2
+(1 row)
+
+SELECT (((SELECT ARRAY[1,2,3])))[3];
+ array 
+-------
+     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 cba449a203df65838e16bbddf0d1e880a10e42b6..8a55474b54a0ea5699011a47545277154835e40d 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 (