PostgreSQL在何处处理 sql查询之十三

继续：

/*--------------------

 * 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;

}

此处调用 query_planner