Github user zellerh commented on a diff in the pull request:
https://github.com/apache/trafodion/pull/1414#discussion_r163898763
--- Diff: core/sql/optimizer/OptPhysRelExpr.cpp ---
@@ -15499,6 +15499,95 @@ GenericUtilExpr::synthPhysicalProperty(const
Context* myContext,
return sppForMe;
} // GenericUtilExpr::synthPhysicalProperty()
+// -----------------------------------------------------------------------
+// FirstN::createContextForAChild()
+// The FirstN node may have an order by requirement that it needs to
+// pass to its child context. Other than that, this method is quite
+// similar to the default implementation, RelExpr::createContextForAChild.
+// The arity of FirstN is always 1, so some logic from the default
+// implementation that deals with childIndex > 0 is unnecessary and has
+// been removed.
+// -----------------------------------------------------------------------
+Context * FirstN::createContextForAChild(Context* myContext,
+ PlanWorkSpace* pws,
+ Lng32& childIndex)
+{
+ const ReqdPhysicalProperty* rppForMe =
+ myContext->getReqdPhysicalProperty();
+
+ CMPASSERT(getArity() == 1);
+
+ childIndex = getArity() - pws->getCountOfChildContexts() - 1;
+
+ // return if we are done
+ if (childIndex < 0)
+ return NULL;
+
+ RequirementGenerator rg(child(childIndex), rppForMe);
+
+ if (reqdOrder().entries() > 0)
+ {
+ // replace our sort requirement with that implied by our ORDER BY
clause
+
+ rg.removeSortKey();
+
+ ValueIdList sortKey;
+ sortKey.insert(reqdOrder());
--- End diff --
Just a nit: It isn't really necessary to make a copy of the required order
here, reqdOrder() could be passed directly to the rg.addSortKey method below?
---
