* any sortgrouprefs specified in its pathtarget, with appropriate
* ressortgroupref labels. This is passed down by parent nodes such as Sort
* and Group, which need these values to be available in their inputs.
+ *
+ * CP_IGNORE_TLIST specifies that the caller plans to replace the targetlist,
+ * and therefore it doens't matter a bit what target list gets generated.
*/
#define CP_EXACT_TLIST 0x0001 /* Plan must return specified tlist */
#define CP_SMALL_TLIST 0x0002 /* Prefer narrower tlists */
#define CP_LABEL_TLIST 0x0004 /* tlist must contain sortgrouprefs */
+#define CP_IGNORE_TLIST 0x0008 /* caller will replace tlist */
static Plan *create_plan_recurse(PlannerInfo *root, Path *best_path,
static Plan *create_unique_plan(PlannerInfo *root, UniquePath *best_path,
int flags);
static Gather *create_gather_plan(PlannerInfo *root, GatherPath *best_path);
-static Plan *create_projection_plan(PlannerInfo *root, ProjectionPath *best_path);
+static Plan *create_projection_plan(PlannerInfo *root,
+ ProjectionPath *best_path,
+ int flags);
static Plan *inject_projection_plan(Plan *subplan, List *tlist, bool parallel_safe);
static Sort *create_sort_plan(PlannerInfo *root, SortPath *best_path, int flags);
static Group *create_group_plan(PlannerInfo *root, GroupPath *best_path);
if (IsA(best_path, ProjectionPath))
{
plan = create_projection_plan(root,
- (ProjectionPath *) best_path);
+ (ProjectionPath *) best_path,
+ flags);
}
else if (IsA(best_path, MinMaxAggPath))
{
* only those Vars actually needed by the query), we prefer to generate a
* tlist containing all Vars in order. This will allow the executor to
* optimize away projection of the table tuples, if possible.
+ *
+ * But if the caller is going to ignore our tlist anyway, then don't
+ * bother generating one at all. We use an exact equality test here, so
+ * that this only applies when CP_IGNORE_TLIST is the only flag set.
*/
- if (use_physical_tlist(root, best_path, flags))
+ if (flags == CP_IGNORE_TLIST)
+ {
+ tlist = NULL;
+ }
+ else if (use_physical_tlist(root, best_path, flags))
{
if (best_path->pathtype == T_IndexOnlyScan)
{
* but sometimes we can just let the subplan do the work.
*/
static Plan *
-create_projection_plan(PlannerInfo *root, ProjectionPath *best_path)
+create_projection_plan(PlannerInfo *root, ProjectionPath *best_path, int flags)
{
Plan *plan;
Plan *subplan;
List *tlist;
+ bool needs_result_node = false;
- /* Since we intend to project, we don't need to constrain child tlist */
- subplan = create_plan_recurse(root, best_path->subpath, 0);
-
- tlist = build_path_tlist(root, &best_path->path);
+ /*
+ * Convert our subpath to a Plan and determine whether we need a Result
+ * node.
+ *
+ * In most cases where we don't need to project, creation_projection_path
+ * will have set dummypp, but not always. First, some createplan.c
+ * routines change the tlists of their nodes. (An example is that
+ * create_merge_append_plan might add resjunk sort columns to a
+ * MergeAppend.) Second, create_projection_path has no way of knowing
+ * what path node will be placed on top of the projection path and
+ * therefore can't predict whether it will require an exact tlist. For
+ * both of these reasons, we have to recheck here.
+ */
+ if (use_physical_tlist(root, &best_path->path, flags))
+ {
+ /*
+ * Our caller doesn't really care what tlist we return, so we don't
+ * actually need to project. However, we may still need to ensure
+ * proper sortgroupref labels, if the caller cares about those.
+ */
+ subplan = create_plan_recurse(root, best_path->subpath, 0);
+ tlist = subplan->targetlist;
+ if ((flags & CP_LABEL_TLIST) != 0)
+ apply_pathtarget_labeling_to_tlist(tlist,
+ best_path->path.pathtarget);
+ }
+ else if (is_projection_capable_path(best_path->subpath))
+ {
+ /*
+ * Our caller requires that we return the exact tlist, but no separate
+ * result node is needed because the subpath is projection-capable.
+ * Tell create_plan_recurse that we're going to ignore the tlist it
+ * produces.
+ */
+ subplan = create_plan_recurse(root, best_path->subpath,
+ CP_IGNORE_TLIST);
+ tlist = build_path_tlist(root, &best_path->path);
+ }
+ else
+ {
+ /*
+ * It looks like we need a result node, unless by good fortune the
+ * requested tlist is exactly the one the child wants to produce.
+ */
+ subplan = create_plan_recurse(root, best_path->subpath, 0);
+ tlist = build_path_tlist(root, &best_path->path);
+ needs_result_node = !tlist_same_exprs(tlist, subplan->targetlist);
+ }
/*
- * We might not really need a Result node here, either because the subplan
- * can project or because it's returning the right list of expressions
- * anyway. Usually create_projection_path will have detected that and set
- * dummypp if we don't need a Result; but its decision can't be final,
- * because some createplan.c routines change the tlists of their nodes.
- * (An example is that create_merge_append_plan might add resjunk sort
- * columns to a MergeAppend.) So we have to recheck here. If we do
- * arrive at a different answer than create_projection_path did, we'll
- * have made slightly wrong cost estimates; but label the plan with the
- * cost estimates we actually used, not "corrected" ones. (XXX this could
- * be cleaned up if we moved more of the sortcolumn setup logic into Path
- * creation, but that would add expense to creating Paths we might end up
- * not using.)
+ * If we make a different decision about whether to include a Result node
+ * than create_projection_path did, we'll have made slightly wrong cost
+ * estimates; but label the plan with the cost estimates we actually used,
+ * not "corrected" ones. (XXX this could be cleaned up if we moved more
+ * of the sortcolumn setup logic into Path creation, but that would add
+ * expense to creating Paths we might end up not using.)
*/
- if (is_projection_capable_path(best_path->subpath) ||
- tlist_same_exprs(tlist, subplan->targetlist))
+ if (!needs_result_node)
{
/* Don't need a separate Result, just assign tlist to subplan */
plan = subplan;
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