PostgreSQL在何处处理 sql查询之十三

/*--------------------
 * grouping_planner
 *      Perform planning steps related to grouping, aggregation, etc.
 *      This primarily means adding top-level processing to the basic
 *      query plan produced by query_planner.
 *
 * tuple_fraction is the fraction of tuples we expect will be retrieved
 *
 * tuple_fraction is interpreted as follows:
 *      0: expect all tuples to be retrieved (normal case)
 *      0 < tuple_fraction < 1: expect the given fraction of tuples available
 *        from the plan to be retrieved
 *      tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
 *        expected to be retrieved (ie, a LIMIT specification)
 *
 * Returns a query plan.  Also, root->query_pathkeys is returned as the
 * actual output ordering of the plan (in pathkey format).
 *--------------------
 */
static Plan *
grouping_planner(PlannerInfo *root, double tuple_fraction)
{
    ...

    if (parse->setOperations)
    {
       ...
    }
    else
    {   

...
        /*
         * Generate the best unsorted and presorted paths for this Query (but
         * note there may not be any presorted path).  query_planner will also
         * estimate the number of groups in the query, and canonicalize all
         * the pathkeys.
         */
        query_planner(root, sub_tlist, tuple_fraction, sub_limit_tuples,
                      &cheapest_path, &sorted_path, &dNumGroups);

        ...
    }                            /* end of if (setOperations) */    ...

    return result_plan;
}