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;
}