PostgreSQL在何处处理 sql查询之十五-优快云博客

本文详细解读了SQL查询中如何通过遍历连接树来构建基本关系RelOptInfo，确保每个非连接RTE在查询中都有对应的基本关系记录，强调了build_simple_rel函数在这一过程中的关键作用。

如此：

接前面，看 add_base_rels_to_query函数：

/*
 * add_base_rels_to_query
 *
 *      Scan the query's jointree and create baserel RelOptInfos for all
 *      the base relations (ie, table, subquery, and function RTEs)
 *      appearing in the jointree.
 *
 * The initial invocation must pass root->parse->jointree as the value of
 * jtnode.    Internally, the function recurses through the jointree.
 *
 * At the end of this process, there should be one baserel RelOptInfo for
 * every non-join RTE that is used in the query.  Therefore, this routine
 * is the only place that should call build_simple_rel with reloptkind
 * RELOPT_BASEREL.    (Note: build_simple_rel recurses internally to build
 * "other rel" RelOptInfos for the members of any appendrels we find here.)
 */
void
add_base_rels_to_query(PlannerInfo *root, Node *jtnode)
{
    if (jtnode == NULL)
        return;
    if (IsA(jtnode, RangeTblRef))
    {
        int            varno = ((RangeTblRef *) jtnode)->rtindex;

        (void) build_simple_rel(root, varno, RELOPT_BASEREL);
    }
    else if (IsA(jtnode, FromExpr))
    {
        FromExpr   *f = (FromExpr *) jtnode;
        ListCell   *l;

        foreach(l, f->fromlist)
            add_base_rels_to_query(root, lfirst(l));
    }
    else if (IsA(jtnode, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) jtnode;

        add_base_rels_to_query(root, j->larg);
        add_base_rels_to_query(root, j->rarg);
    }
    else
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(jtnode));
}