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Commit670a6c7

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Fix grammar for subscripting or field selection from a sub-SELECT result.
Such cases should work, but the grammar failed to accept them because ofour ancient precedence hacks to convince bison that extra parenthesesaround a sub-SELECT in an expression are unambiguous. (Formally, they*are* ambiguous, but we don't especially care whether they're treated aspart 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 viaprecedence declarations is more dangerous than it looks: you can easilycause the parser to reject cases that should work.This has been wrong since commit3db4056or maybe before, and apparently some people have been working around itby inserting no-op casts. That method introduces a dump/reload hazard,as illustrated in bug #7838 from Jan Mate. Hence, back-patch to allactive branches.
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‎src/backend/parser/gram.y

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@@ -10839,6 +10839,29 @@ c_expr:columnref{ $$ = $1; }
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n->location = @1;
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$$ = (Node *)n;
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}
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| select_with_parens indirection
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{
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/*
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* Because the select_with_parens nonterminal is designed
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* to "eat" as many levels of parens as possible, the
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* '(' a_expr ')' opt_indirection production above will
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* fail to match a sub-SELECT with indirection decoration;
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* the sub-SELECT won't be regarded as an a_expr as long
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* as there are parens around it. To support applying
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* subscripting or field selection to a sub-SELECT result,
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* we need this redundant-looking production.
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*/
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SubLink *n =makeNode(SubLink);
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A_Indirection *a =makeNode(A_Indirection);
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n->subLinkType = EXPR_SUBLINK;
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n->testexpr =NULL;
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n->operName = NIL;
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n->subselect = $1;
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n->location = @1;
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a->arg = (Node *)n;
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a->indirection =check_indirection($2, yyscanner);
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$$ = (Node *)a;
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}
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| EXISTS select_with_parens
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{
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SubLink *n =makeNode(SubLink);

‎src/test/regress/expected/subselect.out

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@@ -17,6 +17,61 @@ SELECT 1 AS zero WHERE 1 IN (SELECT 2);
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------
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(0 rows)
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-- Check grammar's handling of extra parens in assorted contexts
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SELECT * FROM (SELECT 1 AS x) ss;
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x
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---
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1
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(1 row)
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SELECT * FROM ((SELECT 1 AS x)) ss;
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x
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---
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1
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(1 row)
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(SELECT 2) UNION SELECT 2;
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?column?
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----------
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2
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(1 row)
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((SELECT 2)) UNION SELECT 2;
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?column?
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----------
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2
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(1 row)
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SELECT ((SELECT 2) UNION SELECT 2);
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?column?
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----------
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2
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(1 row)
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SELECT (((SELECT 2)) UNION SELECT 2);
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?column?
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----------
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2
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(1 row)
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SELECT (SELECT ARRAY[1,2,3])[1];
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array
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-------
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1
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(1 row)
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SELECT ((SELECT ARRAY[1,2,3]))[2];
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array
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-------
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2
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(1 row)
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SELECT (((SELECT ARRAY[1,2,3])))[3];
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array
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-------
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3
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(1 row)
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-- Set up some simple test tables
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CREATE TABLE SUBSELECT_TBL (
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f1 integer,

‎src/test/regress/sql/subselect.sql

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@@ -8,6 +8,21 @@ SELECT 1 AS zero WHERE 1 NOT IN (SELECT 1);
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SELECT1AS zeroWHERE1IN (SELECT2);
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-- Check grammar's handling of extra parens in assorted contexts
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SELECT*FROM (SELECT1AS x) ss;
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SELECT*FROM ((SELECT1AS x)) ss;
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(SELECT2)UNIONSELECT2;
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((SELECT2))UNIONSELECT2;
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SELECT ((SELECT2)UNIONSELECT2);
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SELECT (((SELECT2))UNIONSELECT2);
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SELECT (SELECT ARRAY[1,2,3])[1];
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SELECT ((SELECT ARRAY[1,2,3]))[2];
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SELECT (((SELECT ARRAY[1,2,3])))[3];
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-- Set up some simple test tables
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CREATETABLESUBSELECT_TBL (

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