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Commit117fa25

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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 todistinguish NULL from a_expr are now handled by tests inside the actionsrather than by separate productions. This allows us to accept querieslike 'SELECT 1 + NULL' without requiring parentheses around the NULL.
1 parente8be8ff commit117fa25

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1 file changed

+66
-61
lines changed

1 file changed

+66
-61
lines changed

‎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
* AUTHORDATEMAJOR EVENT
@@ -77,6 +77,7 @@ static Node *makeTypeCast(Node *arg, TypeName *typename);
7777
static Node *makeRowExpr(char *opr, List *largs, List *rargs);
7878
staticvoidmapTargetColumns(List *source, List *target);
7979
staticvoidparam_type_init(Oid *typev,int nargs);
80+
staticboolexprIsNullConstant(Node *arg);
8081
static Node *doNegate(Node *n);
8182
staticvoiddoNegateFloat(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-
SETDEFAULTa_expr{$$ =$3; }
877-
|SETDEFAULTNULL_P{$$ =NULL; }
877+
SETDEFAULTa_expr
878+
{
879+
/* Treat SET DEFAULT NULL the same as DROP DEFAULT*/
880+
if (exprIsNullConstant($3))
881+
$$ =NULL;
882+
else
883+
$$ =$3;
884+
}
878885
|DROPDEFAULT{$$ =NULL; }
879886
;
880887

@@ -1155,22 +1162,20 @@ ColConstraintElem:
11551162
n->keys =NULL;
11561163
$$ = (Node *)n;
11571164
}
1158-
|DEFAULTNULL_P
1159-
{
1160-
Constraint *n = makeNode(Constraint);
1161-
n->contype = CONSTR_DEFAULT;
1162-
n->name =NULL;
1163-
n->raw_expr =NULL;
1164-
n->cooked_expr =NULL;
1165-
n->keys =NULL;
1166-
$$ = (Node *)n;
1167-
}
11681165
|DEFAULTb_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
{$$ =$1; }
41384133
|a_exprTYPECASTTypename
41394134
{$$ = 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_PTYPECASTTypename
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+
$$ = makeA_Expr(ISNULL,NULL,$1,NULL);
4189+
elseif (exprIsNullConstant($1))
4190+
$$ = makeA_Expr(ISNULL,NULL,$3,NULL);
4191+
else
4192+
$$ = makeA_Expr(OP,"=",$1,$3);
4193+
}
42054194

42064195
|a_exprOpa_expr
42074196
{$$ = makeA_Expr(OP,$2,$1,$3); }
@@ -4360,21 +4349,14 @@ a_expr: c_expr
43604349
*
43614350
* b_expr is a subset of the complete expression syntax defined by a_expr.
43624351
*
4363-
* Presently, AND, NOT, IS,IN,andNULL are the a_expr keywords that would
4352+
* Presently, AND, NOT, IS, andIN are the a_expr keywords that would
43644353
* cause trouble in the places where b_expr is used. For simplicity, we
43654354
* just eliminate all the boolean-keyword-operator productions from b_expr.
43664355
*/
43674356
b_expr:c_expr
43684357
{$$ =$1; }
43694358
|b_exprTYPECASTTypename
43704359
{$$ = makeTypeCast($1,$3); }
4371-
|NULL_PTYPECASTTypename
4372-
{
4373-
A_Const *n = makeNode(A_Const);
4374-
n->val.type = T_Null;
4375-
n->typename =$3;
4376-
$$ = (Node *)n;
4377-
}
43784360
|'-'b_expr %precUMINUS
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
{$$ =$2; }
4447-
|CAST'('a_expr_or_nullASTypename')'
4429+
|CAST'('a_exprASTypename')'
44484430
{$$ = 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_listUSINGa_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:WHENa_exprTHENa_expr_or_null
4913+
when_clause:WHENa_exprTHENa_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:ELSEa_expr_or_null{$$ =$2; }
4922+
case_default:ELSEa_expr{$$ =$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_nullASColLabel
4974+
target_el:a_exprASColLabel
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:ColIdopt_indirection'='a_expr_or_null
5022+
update_target_el:ColIdopt_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:PARAMopt_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+
staticbool
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+
returntrue;
5536+
}
5537+
returnfalse;
5538+
}
5539+
55355540
/*
55365541
* doNegate --- handle negation of a numeric constant.
55375542
*

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