PostgreSQL在何处处理 sql查询之二十五

再次梳理  build_simple_rel 的执行内容：

/*
 * build_simple_rel
 *      Construct a new RelOptInfo for a base relation or 'other' relation.
 */
RelOptInfo *
build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
{
    RelOptInfo *rel;
    RangeTblEntry *rte;

    /* Rel should not exist already */
    Assert(relid > 0 && relid < root->simple_rel_array_size);
    if (root->simple_rel_array[relid] != NULL)
        elog(ERROR, "rel %d already exists", relid);

    /* Fetch RTE for relation */
    rte = root->simple_rte_array[relid];
    Assert(rte != NULL);

    rel = makeNode(RelOptInfo);
    rel->reloptkind = reloptkind;
    rel->relids = bms_make_singleton(relid);
    rel->rows = 0;
    ...
    rel->has_eclass_joins = false;

    /* Check type of rtable entry */
    switch (rte->rtekind)
    {
        case RTE_RELATION:
            /* Table --- retrieve statistics from the system catalogs */
            get_relation_info(root, rte->relid, rte->inh, rel);
            break;
        case RTE_SUBQUERY:
        case RTE_FUNCTION:
        case RTE_VALUES:
        case RTE_CTE:

            /*
             * Subquery, function, or values list --- set up attr range and
             * arrays
             *
             * Note: 0 is included in range to support whole-row Vars
             */
            rel->min_attr = 0;
            rel->max_attr = list_length(rte->eref->colnames);
            rel->attr_needed = (Relids *)
                palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(Relids));
            rel->attr_widths = (int32 *)
                palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(int32));
            break;
        default:
            elog(ERROR, "unrecognized RTE kind: %d",
                 (int) rte->rtekind);
            break;
    }

    /* Save the finished struct in the query's simple_rel_array */
    root->simple_rel_array[relid] = rel;

    ...
    return rel;
}

可以看出，这是准备了 表信息的结构--RelOptInfo，然后再把它挂在计划树上：

    root->simple_rel_array[relid] = rel;

 需要注意的是，这里 relid 是 simple_rel_array数组的下标，而非oid。