繼續(xù)：

/*--------------------* 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; }

此處調(diào)用 query_planner

轉(zhuǎn)載于:https://www.cnblogs.com/gaojian/archive/2013/05/23/3094769.html

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