@ -11,7 +11,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.214 2001/01/06 10:50:02 petere Exp $
* $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.215 2001/01/15 20:36:36 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@ -146,7 +146,8 @@ static void doNegateFloat(Value *v);
UnlistenStmt, UpdateStmt, VacuumStmt, VariableResetStmt,
VariableSetStmt, VariableShowStmt, ViewStmt, CheckPointStmt
%type <node> select_no_parens, select_clause, simple_select
%type <node> select_no_parens, select_with_parens, select_clause,
simple_select
%type <node> alter_column_action
%type <ival> drop_behavior
@ -2666,16 +2667,7 @@ RuleActionMulti: RuleActionMulti ';' RuleActionStmtOrEmpty
}
;
/*
* Allowing RuleActionStmt to be a SelectStmt creates an ambiguity:
* is the RuleActionList "((SELECT foo))" a standalone RuleActionStmt,
* or a one-entry RuleActionMulti list? We don't really care, but yacc
* wants to know. We use operator precedence to resolve the ambiguity:
* giving this rule a higher precedence than ')' will force a reduce
* rather than shift decision, causing the one-entry-list interpretation
* to be chosen.
*/
RuleActionStmt: SelectStmt %prec TYPECAST
RuleActionStmt: SelectStmt
| InsertStmt
| UpdateStmt
| DeleteStmt
@ -3262,32 +3254,48 @@ opt_cursor: BINARY { $$ = TRUE; }
* The rule returns either a single SelectStmt node or a tree of them,
* representing a set-operation tree.
*
* To avoid ambiguity problems with nested parentheses, we have to define
* a "select_no_parens" nonterminal in which there are no parentheses
* at the outermost level. This is used in the production
* c_expr: '(' select_no_parens ')'
* This gives a unique parsing of constructs where a subselect is nested
* in an expression with extra parentheses: the parentheses are not part
* of the subselect but of the outer expression. yacc is not quite bright
* enough to handle the situation completely, however. To prevent a shift/
* reduce conflict, we also have to attach a precedence to the
* SelectStmt: select_no_parens
* rule that is higher than the precedence of ')'. This means that when
* "((SELECT foo" has been parsed in an expression context, and the
* next token is ')', the parser will follow the '(' SelectStmt ')' reduction
* path rather than '(' select_no_parens ')'. The upshot is that excess
* parens don't work in this context: SELECT ((SELECT foo)) will give a
* parse error, whereas SELECT ((SELECT foo) UNION (SELECT bar)) is OK.
* This is ugly, but it beats not allowing excess parens anywhere...
*
* In all other contexts, we can use SelectStmt which allows outer parens.
* There is an ambiguity when a sub-SELECT is within an a_expr and there
* are excess parentheses: do the parentheses belong to the sub-SELECT or
* to the surrounding a_expr? We don't really care, but yacc wants to know.
* To resolve the ambiguity, we are careful to define the grammar so that
* the decision is staved off as long as possible: as long as we can keep
* absorbing parentheses into the sub-SELECT, we will do so, and only when
* it's no longer possible to do that will we decide that parens belong to
* the expression. For example, in "SELECT (((SELECT 2)) + 3)" the extra
* parentheses are treated as part of the sub-select. The necessity of doing
* it that way is shown by "SELECT (((SELECT 2)) UNION SELECT 2)". Had we
* parsed "((SELECT 2))" as an a_expr, it'd be too late to go back to the
* SELECT viewpoint when we see the UNION.
*
* This approach is implemented by defining a nonterminal select_with_parens,
* which represents a SELECT with at least one outer layer of parentheses,
* and being careful to use select_with_parens, never '(' SelectStmt ')',
* in the expression grammar. We will then have shift-reduce conflicts
* which we can resolve in favor of always treating '(' <select> ')' as
* a select_with_parens. To resolve the conflicts, the productions that
* conflict with the select_with_parens productions are manually given
* precedences lower than the precedence of ')', thereby ensuring that we
* shift ')' (and then reduce to select_with_parens) rather than trying to
* reduce the inner <select> nonterminal to something else. We use UMINUS
* precedence for this, which is a fairly arbitrary choice.
*
* To be able to define select_with_parens itself without ambiguity, we need
* a nonterminal select_no_parens that represents a SELECT structure with no
* outermost parentheses. This is a little bit tedious, but it works.
*
* In non-expression contexts, we use SelectStmt which can represent a SELECT
* with or without outer parentheses.
*/
SelectStmt: select_no_parens %prec TYPECAST
SelectStmt: select_no_parens %prec UMINUS
| select_with_parens %prec UMINUS
;
select_with_parens: '(' select_no_parens ')'
{
$$ = $1;
$$ = $2 ;
}
| '(' SelectStmt ')'
| '(' select_with_parens ')'
{
$$ = $2;
}
@ -3318,13 +3326,7 @@ select_no_parens: simple_select
;
select_clause: simple_select
{
$$ = $1;
}
| '(' SelectStmt ')'
{
$$ = $2;
}
| select_with_parens
;
/*
@ -3342,8 +3344,10 @@ select_clause: simple_select
* (SELECT foo UNION SELECT bar) ORDER BY baz
* not
* SELECT foo UNION (SELECT bar ORDER BY baz)
* Likewise FOR UPDATE and LIMIT. This does not limit functionality,
* because you can reintroduce sort and limit clauses inside parentheses.
* Likewise FOR UPDATE and LIMIT. Therefore, those clauses are described
* as part of the select_no_parens production, not simple_select.
* This does not limit functionality, because you can reintroduce sort and
* limit clauses inside parentheses.
*
* NOTE: only the leftmost component SelectStmt should have INTO.
* However, this is not checked by the grammar; parse analysis must check it.
@ -3614,11 +3618,11 @@ table_ref: relation_expr
$1->name = $2;
$$ = (Node *) $1;
}
| '(' SelectStmt ')' alias_clause
| select_with_parens alias_clause
{
RangeSubselect *n = makeNode(RangeSubselect);
n->subquery = $2 ;
n->name = $4 ;
n->subquery = $1 ;
n->name = $2 ;
$$ = (Node *) n;
}
| joined_table
@ -3788,7 +3792,7 @@ relation_expr: relation_name
$$->inhOpt = INH_DEFAULT;
$$->name = NULL;
}
| relation_name '*' %prec '='
| relation_name '*'
{
/* inheritance query */
$$ = makeNode(RangeVar);
@ -3796,7 +3800,7 @@ relation_expr: relation_name
$$->inhOpt = INH_YES;
$$->name = NULL;
}
| ONLY relation_name %prec '='
| ONLY relation_name
{
/* no inheritance */
$$ = makeNode(RangeVar);
@ -4146,27 +4150,27 @@ opt_interval: datetime { $$ = makeList1($1); }
* Define row_descriptor to allow yacc to break the reduce/reduce conflict
* with singleton expressions.
*/
row_expr: '(' row_descriptor ')' IN '(' SelectStmt ')'
row_expr: '(' row_descriptor ')' IN select_with_parens
{
SubLink *n = makeNode(SubLink);
n->lefthand = $2;
n->oper = (List *) makeA_Expr(OP, "=", NULL, NULL);
n->useor = FALSE;
n->subLinkType = ANY_SUBLINK;
n->subselect = $6 ;
n->subselect = $5 ;
$$ = (Node *)n;
}
| '(' row_descriptor ')' NOT IN '(' SelectStmt ')'
| '(' row_descriptor ')' NOT IN select_with_parens
{
SubLink *n = makeNode(SubLink);
n->lefthand = $2;
n->oper = (List *) makeA_Expr(OP, "<>", NULL, NULL);
n->useor = TRUE;
n->subLinkType = ALL_SUBLINK;
n->subselect = $7 ;
n->subselect = $6 ;
$$ = (Node *)n;
}
| '(' row_descriptor ')' all_Op sub_type '(' SelectStmt ')'
| '(' row_descriptor ')' all_Op sub_type select_with_parens
{
SubLink *n = makeNode(SubLink);
n->lefthand = $2;
@ -4176,10 +4180,10 @@ row_expr: '(' row_descriptor ')' IN '(' SelectStmt ')'
else
n->useor = FALSE;
n->subLinkType = $5;
n->subselect = $7 ;
n->subselect = $6 ;
$$ = (Node *)n;
}
| '(' row_descriptor ')' all_Op '(' SelectStmt ')'
| '(' row_descriptor ')' all_Op select_with_parens
{
SubLink *n = makeNode(SubLink);
n->lefthand = $2;
@ -4189,7 +4193,7 @@ row_expr: '(' row_descriptor ')' IN '(' SelectStmt ')'
else
n->useor = FALSE;
n->subLinkType = MULTIEXPR_SUBLINK;
n->subselect = $6 ;
n->subselect = $5 ;
$$ = (Node *)n;
}
| '(' row_descriptor ')' all_Op '(' row_descriptor ')'
@ -4291,9 +4295,9 @@ a_expr: c_expr
* If you add more explicitly-known operators, be sure to add them
* also to b_expr and to the MathOp list above.
*/
| '+' a_expr %prec UMINUS
| '+' a_expr %prec UMINUS
{ $$ = makeA_Expr(OP, "+", NULL, $2); }
| '-' a_expr %prec UMINUS
| '-' a_expr %prec UMINUS
{ $$ = doNegate($2); }
| '%' a_expr
{ $$ = makeA_Expr(OP, "%", NULL, $2); }
@ -4458,12 +4462,12 @@ a_expr: c_expr
makeA_Expr(OP, "<", $1, $4),
makeA_Expr(OP, ">", $1, $6));
}
| a_expr IN '(' in_expr ')'
| a_expr IN in_expr
{
/* in_expr returns a SubLink or a list of a_exprs */
if (IsA($4 , SubLink))
if (IsA($3 , SubLink))
{
SubLink *n = (SubLink *)$4 ;
SubLink *n = (SubLink *)$3 ;
n->lefthand = makeList1($1);
n->oper = (List *) makeA_Expr(OP, "=", NULL, NULL);
n->useor = FALSE;
@ -4474,7 +4478,7 @@ a_expr: c_expr
{
Node *n = NULL;
List *l;
foreach(l, (List *) $4 )
foreach(l, (List *) $3 )
{
Node *cmp = makeA_Expr(OP, "=", $1, lfirst(l));
if (n == NULL)
@ -4485,12 +4489,12 @@ a_expr: c_expr
$$ = n;
}
}
| a_expr NOT IN '(' in_expr ')'
| a_expr NOT IN in_expr
{
/* in_expr returns a SubLink or a list of a_exprs */
if (IsA($5 , SubLink))
if (IsA($4 , SubLink))
{
SubLink *n = (SubLink *)$5 ;
SubLink *n = (SubLink *)$4 ;
n->lefthand = makeList1($1);
n->oper = (List *) makeA_Expr(OP, "<>", NULL, NULL);
n->useor = FALSE;
@ -4501,7 +4505,7 @@ a_expr: c_expr
{
Node *n = NULL;
List *l;
foreach(l, (List *) $5 )
foreach(l, (List *) $4 )
{
Node *cmp = makeA_Expr(OP, "<>", $1, lfirst(l));
if (n == NULL)
@ -4512,14 +4516,14 @@ a_expr: c_expr
$$ = n;
}
}
| a_expr all_Op sub_type '(' SelectStmt ')'
| a_expr all_Op sub_type select_with_parens
{
SubLink *n = makeNode(SubLink);
n->lefthand = makeList1($1);
n->oper = (List *) makeA_Expr(OP, $2, NULL, NULL);
n->useor = FALSE; /* doesn't matter since only one col */
n->subLinkType = $3;
n->subselect = $5 ;
n->subselect = $4 ;
$$ = (Node *)n;
}
| row_expr
@ -4539,9 +4543,9 @@ b_expr: c_expr
{ $$ = $1; }
| b_expr TYPECAST Typename
{ $$ = makeTypeCast($1, $3); }
| '+' b_expr %prec UMINUS
| '+' b_expr %prec UMINUS
{ $$ = makeA_Expr(OP, "+", NULL, $2); }
| '-' b_expr %prec UMINUS
| '-' b_expr %prec UMINUS
{ $$ = doNegate($2); }
| '%' b_expr
{ $$ = makeA_Expr(OP, "%", NULL, $2); }
@ -4908,24 +4912,24 @@ c_expr: attr
n->agg_distinct = FALSE;
$$ = (Node *)n;
}
| '(' select_no_parens ')'
| select_with_parens %prec UMINUS
{
SubLink *n = makeNode(SubLink);
n->lefthand = NIL;
n->oper = NIL;
n->useor = FALSE;
n->subLinkType = EXPR_SUBLINK;
n->subselect = $2 ;
n->subselect = $1 ;
$$ = (Node *)n;
}
| EXISTS '(' SelectStmt ')'
| EXISTS select_with_parens
{
SubLink *n = makeNode(SubLink);
n->lefthand = NIL;
n->oper = NIL;
n->useor = FALSE;
n->subLinkType = EXISTS_SUBLINK;
n->subselect = $3 ;
n->subselect = $2 ;
$$ = (Node *)n;
}
;
@ -5037,14 +5041,14 @@ trim_list: a_expr FROM expr_list
{ $$ = $1; }
;
in_expr: SelectStmt
in_expr: select_with_parens
{
SubLink *n = makeNode(SubLink);
n->subselect = $1;
$$ = (Node *)n;
}
| in_expr_nodes
{ $$ = (Node *)$1 ; }
| '(' in_expr_nodes ')'
{ $$ = (Node *)$2 ; }
;
in_expr_nodes: a_expr
Tom Lane
25 years ago