/*--------------------* subquery_planner*      Invokes the planner on a subquery.  We recurse to here for each*      sub-SELECT found in the query tree.** glob is the global state for the current planner run.* parse is the querytree produced by the parser & rewriter.* parent_root is the immediate parent Query's info (NULL at the top level).* hasRecursion is true if this is a recursive WITH query.* tuple_fraction is the fraction of tuples we expect will be retrieved.* tuple_fraction is interpreted as explained for grouping_planner, below.** If subroot isn't NULL, we pass back the query's final PlannerInfo struct;* among other things this tells the output sort ordering of the plan.** Basically, this routine does the stuff that should only be done once* per Query object.  It then calls grouping_planner.  At one time,* grouping_planner could be invoked recursively on the same Query object;* that's not currently true, but we keep the separation between the two* routines anyway, in case we need it again someday.** subquery_planner will be called recursively to handle sub-Query nodes* found within the query's expressions and rangetable.** Returns a query plan.*--------------------*/
Plan *
subquery_planner(PlannerGlobal *glob, Query *parse,PlannerInfo *parent_root,bool hasRecursion, double tuple_fraction,PlannerInfo **subroot)
{
   .../** Do the main planning.  If we have an inherited target relation, that* needs special processing, else go straight to grouping_planner.*/if (parse->resultRelation &&rt_fetch(parse->resultRelation, parse->rtable)->inh)plan = inheritance_planner(root);else{
        plan = grouping_planner(root, tuple_fraction);/* If it's not SELECT, we need a ModifyTable node */if (parse->commandType != CMD_SELECT){List       *returningLists;List       *rowMarks;/** Set up the RETURNING list-of-lists, if needed.*/if (parse->returningList)returningLists = list_make1(parse->returningList);elsereturningLists = NIL;/** If there was a FOR UPDATE/SHARE clause, the LockRows node will* have dealt with fetching non-locked marked rows, else we need* to have ModifyTable do that.*/if (parse->rowMarks)rowMarks = NIL;elserowMarks = root->rowMarks;
plan = (Plan *) make_modifytable(parse->commandType,parse->canSetTag,list_make1_int(parse->resultRelation),list_make1(plan),returningLists,rowMarks,SS_assign_special_param(root));}}
    ...return plan;
}