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Clean up grammar's handling of NULL in expressions: a_expr_or_null is
gone, replaced by plain a_expr. The few places where we needed to distinguish NULL from a_expr are now handled by tests inside the actions rather than by separate productions. This allows us to accept queries like 'SELECT 1 + NULL' without requiring parentheses around the NULL.
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‎src/backend/parser/gram.y

Lines changed: 66 additions & 61 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
*
1212
*
1313
* IDENTIFICATION
14-
* $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.153 2000/03/01 05:18:19 tgl Exp $
14+
* $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.154 2000/03/12 00:39:52 tgl Exp $
1515
*
1616
* HISTORY
1717
* AUTHOR DATE MAJOR EVENT
@@ -77,6 +77,7 @@ static Node *makeTypeCast(Node *arg, TypeName *typename);
7777
static Node *makeRowExpr(char *opr, List *largs, List *rargs);
7878
static void mapTargetColumns(List *source, List *target);
7979
static void param_type_init(Oid *typev, int nargs);
80+
static bool exprIsNullConstant(Node *arg);
8081
static Node *doNegate(Node *n);
8182
static void doNegateFloat(Value *v);
8283

@@ -229,7 +230,7 @@ static void doNegateFloat(Value *v);
229230
%type <node> columnDef
230231
%type <defelt> def_elem
231232
%type <node> def_arg, columnElem, where_clause,
232-
a_expr, a_expr_or_null, b_expr, c_expr, AexprConst,
233+
a_expr, b_expr, c_expr, AexprConst,
233234
in_expr, having_clause
234235
%type <list> row_descriptor, row_list, in_expr_nodes
235236
%type <node> row_expr
@@ -873,8 +874,14 @@ AlterTableStmt:
873874
;
874875

875876
alter_column_action:
876-
SET DEFAULT a_expr { $$ = $3; }
877-
| SET DEFAULT NULL_P { $$ = NULL; }
877+
SET DEFAULT a_expr
878+
{
879+
/* Treat SET DEFAULT NULL the same as DROP DEFAULT */
880+
if (exprIsNullConstant($3))
881+
$$ = NULL;
882+
else
883+
$$ = $3;
884+
}
878885
| DROP DEFAULT { $$ = NULL; }
879886
;
880887

@@ -1155,22 +1162,20 @@ ColConstraintElem:
11551162
n->keys = NULL;
11561163
$$ = (Node *)n;
11571164
}
1158-
| DEFAULT NULL_P
1159-
{
1160-
Constraint *n = makeNode(Constraint);
1161-
n->contype = CONSTR_DEFAULT;
1162-
n->name = NULL;
1163-
n->raw_expr = NULL;
1164-
n->cooked_expr = NULL;
1165-
n->keys = NULL;
1166-
$$ = (Node *)n;
1167-
}
11681165
| DEFAULT b_expr
11691166
{
11701167
Constraint *n = makeNode(Constraint);
11711168
n->contype = CONSTR_DEFAULT;
11721169
n->name = NULL;
1173-
n->raw_expr = $2;
1170+
if (exprIsNullConstant($2))
1171+
{
1172+
/* DEFAULT NULL should be reported as empty expr */
1173+
n->raw_expr = NULL;
1174+
}
1175+
else
1176+
{
1177+
n->raw_expr = $2;
1178+
}
11741179
n->cooked_expr = NULL;
11751180
n->keys = NULL;
11761181
$$ = (Node *)n;
@@ -4017,16 +4022,6 @@ opt_interval: datetime { $$ = lcons($1, NIL); }
40174022
*
40184023
*****************************************************************************/
40194024

4020-
a_expr_or_null: a_expr
4021-
{ $$ = $1; }
4022-
| NULL_P
4023-
{
4024-
A_Const *n = makeNode(A_Const);
4025-
n->val.type = T_Null;
4026-
$$ = (Node *)n;
4027-
}
4028-
;
4029-
40304025
/* Expressions using row descriptors
40314026
* Define row_descriptor to allow yacc to break the reduce/reduce conflict
40324027
* with singleton expressions.
@@ -4137,17 +4132,6 @@ a_expr: c_expr
41374132
{ $$ = $1; }
41384133
| a_expr TYPECAST Typename
41394134
{ $$ = makeTypeCast($1, $3); }
4140-
/*
4141-
* Can't collapse this into prior rule by using a_expr_or_null;
4142-
* that creates reduce/reduce conflicts. Grumble.
4143-
*/
4144-
| NULL_P TYPECAST Typename
4145-
{
4146-
A_Const *n = makeNode(A_Const);
4147-
n->val.type = T_Null;
4148-
n->typename = $3;
4149-
$$ = (Node *)n;
4150-
}
41514135
/*
41524136
* These operators must be called out explicitly in order to make use
41534137
* of yacc/bison's automatic operator-precedence handling. All other
@@ -4193,15 +4177,20 @@ a_expr: c_expr
41934177
{ $$ = makeA_Expr(OP, "<", $1, $3); }
41944178
| a_expr '>' a_expr
41954179
{ $$ = makeA_Expr(OP, ">", $1, $3); }
4196-
4197-
| a_expr '=' NULL_P
4198-
{ $$ = makeA_Expr(ISNULL, NULL, $1, NULL); }
4199-
/* We allow this for standards-broken SQL products, like MS stuff */
4200-
| NULL_P '=' a_expr
4201-
{ $$ = makeA_Expr(ISNULL, NULL, $3, NULL); }
4202-
42034180
| a_expr '=' a_expr
4204-
{ $$ = makeA_Expr(OP, "=", $1, $3); }
4181+
{
4182+
/*
4183+
* Special-case "foo = NULL" and "NULL = foo" for
4184+
* compatibility with standards-broken products
4185+
* (like Microsoft's). Turn these into IS NULL exprs.
4186+
*/
4187+
if (exprIsNullConstant($3))
4188+
$$ = makeA_Expr(ISNULL, NULL, $1, NULL);
4189+
else if (exprIsNullConstant($1))
4190+
$$ = makeA_Expr(ISNULL, NULL, $3, NULL);
4191+
else
4192+
$$ = makeA_Expr(OP, "=", $1, $3);
4193+
}
42054194

42064195
| a_expr Op a_expr
42074196
{ $$ = makeA_Expr(OP, $2, $1, $3); }
@@ -4360,21 +4349,14 @@ a_expr: c_expr
43604349
*
43614350
* b_expr is a subset of the complete expression syntax defined by a_expr.
43624351
*
4363-
* Presently, AND, NOT, IS, IN, and NULL are the a_expr keywords that would
4352+
* Presently, AND, NOT, IS, and IN are the a_expr keywords that would
43644353
* cause trouble in the places where b_expr is used. For simplicity, we
43654354
* just eliminate all the boolean-keyword-operator productions from b_expr.
43664355
*/
43674356
b_expr: c_expr
43684357
{ $$ = $1; }
43694358
| b_expr TYPECAST Typename
43704359
{ $$ = makeTypeCast($1, $3); }
4371-
| NULL_P TYPECAST Typename
4372-
{
4373-
A_Const *n = makeNode(A_Const);
4374-
n->val.type = T_Null;
4375-
n->typename = $3;
4376-
$$ = (Node *)n;
4377-
}
43784360
| '-' b_expr %prec UMINUS
43794361
{ $$ = doNegate($2); }
43804362
| '%' b_expr
@@ -4442,9 +4424,9 @@ c_expr: attr
44424424
}
44434425
| AexprConst
44444426
{ $$ = $1; }
4445-
| '(' a_expr_or_null ')'
4427+
| '(' a_expr ')'
44464428
{ $$ = $2; }
4447-
| CAST '(' a_expr_or_null AS Typename ')'
4429+
| CAST '(' a_expr AS Typename ')'
44484430
{ $$ = makeTypeCast($3, $5); }
44494431
| case_expr
44504432
{ $$ = $1; }
@@ -4788,9 +4770,9 @@ opt_indirection: '[' a_expr ']' opt_indirection
47884770
{ $$ = NIL; }
47894771
;
47904772

4791-
expr_list: a_expr_or_null
4773+
expr_list: a_expr
47924774
{ $$ = lcons($1, NIL); }
4793-
| expr_list ',' a_expr_or_null
4775+
| expr_list ',' a_expr
47944776
{ $$ = lappend($1, $3); }
47954777
| expr_list USING a_expr
47964778
{ $$ = lappend($1, $3); }
@@ -4928,7 +4910,7 @@ when_clause_list: when_clause_list when_clause
49284910
{ $$ = lcons($1, NIL); }
49294911
;
49304912

4931-
when_clause: WHEN a_expr THEN a_expr_or_null
4913+
when_clause: WHEN a_expr THEN a_expr
49324914
{
49334915
CaseWhen *w = makeNode(CaseWhen);
49344916
w->expr = $2;
@@ -4937,7 +4919,7 @@ when_clause: WHEN a_expr THEN a_expr_or_null
49374919
}
49384920
;
49394921

4940-
case_default: ELSE a_expr_or_null { $$ = $2; }
4922+
case_default: ELSE a_expr { $$ = $2; }
49414923
| /*EMPTY*/ { $$ = NULL; }
49424924
;
49434925

@@ -4989,14 +4971,14 @@ target_list: target_list ',' target_el
49894971
;
49904972

49914973
/* AS is not optional because shift/red conflict with unary ops */
4992-
target_el: a_expr_or_null AS ColLabel
4974+
target_el: a_expr AS ColLabel
49934975
{
49944976
$$ = makeNode(ResTarget);
49954977
$$->name = $3;
49964978
$$->indirection = NULL;
49974979
$$->val = (Node *)$1;
49984980
}
4999-
| a_expr_or_null
4981+
| a_expr
50004982
{
50014983
$$ = makeNode(ResTarget);
50024984
$$->name = NULL;
@@ -5037,7 +5019,7 @@ update_target_list: update_target_list ',' update_target_el
50375019
{ $$ = lcons($1, NIL); }
50385020
;
50395021

5040-
update_target_el: ColId opt_indirection '=' a_expr_or_null
5022+
update_target_el: ColId opt_indirection '=' a_expr
50415023
{
50425024
$$ = makeNode(ResTarget);
50435025
$$->name = $1;
@@ -5142,6 +5124,12 @@ AexprConst: Iconst
51425124
n->typename->typmod = -1;
51435125
$$ = (Node *)n;
51445126
}
5127+
| NULL_P
5128+
{
5129+
A_Const *n = makeNode(A_Const);
5130+
n->val.type = T_Null;
5131+
$$ = (Node *)n;
5132+
}
51455133
;
51465134

51475135
ParamNo: PARAM opt_indirection
@@ -5532,6 +5520,23 @@ Oid param_type(int t)
55325520
return param_type_info[t - 1];
55335521
}
55345522

5523+
/*
5524+
* Test whether an a_expr is a plain NULL constant or not.
5525+
*/
5526+
static bool
5527+
exprIsNullConstant(Node *arg)
5528+
{
5529+
if (arg && IsA(arg, A_Const))
5530+
{
5531+
A_Const *con = (A_Const *) arg;
5532+
5533+
if (con->val.type == T_Null &&
5534+
con->typename == NULL)
5535+
return true;
5536+
}
5537+
return false;
5538+
}
5539+
55355540
/*
55365541
* doNegate --- handle negation of a numeric constant.
55375542
*

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