修改gram.y 的select 部分，看能否找出 target_list中的 各个字段名称：
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simple_select:
SELECT opt_distinct target_list
into_clause from_clause where_clause
group_clause having_clause window_clause
{
SelectStmt *n = makeNode(SelectStmt);
n->distinctClause = $2;
n->targetList = $3;
n->intoClause = $4;
n->fromClause = $5;
n->whereClause = $6;
n->groupClause = $7;
n->havingClause = $8;
n->windowClause = $9;
$$ = (Node *)n;
ListCell * curr=n->targetList->head;
while ( curr != NULL)
{
//To display the current ResTarget Node
if (curr->data.ptr_value==NULL)
fprintf(stderr,"NULL of ptr_value\n");
else
fprintf(stderr,"Not NULL of ptr_value\n");
ResTarget * restar=(ResTarget *)(curr->data.ptr_value);
Node * nod=(Node *)(restar->val);
ColumnRef * colref=(ColumnRef *)nod;
if (colref ==NULL)
fprintf(stderr,"NULL of ColumnRef\n");
else
fprintf(stderr,"Not NULL of ColumnRef\n");
Value * vval=(Value *)(colref->fields->head->data.ptr_value);
if (vval == NULL)
fprintf(stderr,"NULl of vval\n");
else
fprintf(stderr,"Not Null of vval\n");
fprintf(stderr,"colum is: %s\n",vval->val.str);
curr=curr->next;
}
}
| values_clause { $$ = $1; }
| TABLE relation_expr
{
/* same as SELECT * FROM relation_expr */
ColumnRef *cr = makeNode(ColumnRef);
ResTarget *rt = makeNode(ResTarget);
SelectStmt *n = makeNode(SelectStmt);
cr->fields = list_make1(makeNode(A_Star));
cr->location = -1;
rt->name = NULL;
rt->indirection = NIL;
rt->val = (Node *)cr;
rt->location = -1;
n->targetList = list_make1(rt);
n->fromClause = list_make1($2);
$$ = (Node *)n;
}
| select_clause UNION opt_all select_clause
{
$$ = makeSetOp(SETOP_UNION, $3, $1, $4);
}
| select_clause INTERSECT opt_all select_clause
{
$$ = makeSetOp(SETOP_INTERSECT, $3, $1, $4);
}
| select_clause EXCEPT opt_all select_clause
{
$$ = makeSetOp(SETOP_EXCEPT, $3, $1, $4);
}
;
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执行sql文的时候，后台能够正确给出 各个字段的名称。
本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/archive/2012/09/11/2680395.html，如需转载请自行联系原作者
