PostgreSQL在何处处理 sql查询之十二

/*--------------------
* 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);
else
returningLists = 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;
else
rowMarks = 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;
}

grouping_planner