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对PostgreSQL语法分析中 targetlist 的理解

2012-09-06 15:39 295 查看

在 gram.y 中:

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;
}

……

把它修改一下，增加：

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;
fprintf(stderr,"length of list: %d\n", n->targetList->length);

}

……

psql 中执行： select id, name from a8;

后台出现： length of list: 2

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