Add support for ORDER BY adn DISTINCT.

This is handled on the Coordinator. It will push down the ORDER BY
and merge-sort the sorted input streams from the nodes.

It converts from DataRow to tuple format as needed.

If one of the SELECT clause expressions is not in the ORDER BY,
it appends it to the ORDER BY when pushing it down to the data nodes
and leaves it off when returning to the client.

With DISTINCT, an ORDER BY will be used and pushed down to the data
nodes such that a merge-sort can be done and de-duplication can
occur.

By Andrei Martsinchyk

1 files changed, 10 insertions, 0 deletions

diff --git a/src/include/utils/tuplesort.h b/src/include/utils/tuplesort.h
index e351536d47..e2b3c033e0 100644
--- a/src/include/utils/tuplesort.h
+++ b/src/include/utils/tuplesort.h
@@ -23,6 +23,9 @@
 #include "access/itup.h"
 #include "executor/tuptable.h"
 #include "fmgr.h"
+#ifdef PGXC
+#include "pgxc/execRemote.h"
+#endif
 #include "utils/relcache.h"
 
 
@@ -64,6 +67,13 @@ extern Tuplesortstate *tuplesort_begin_index_hash(Relation indexRel,
 extern Tuplesortstate *tuplesort_begin_datum(Oid datumType,
 					  Oid sortOperator, bool nullsFirstFlag,
 					  int workMem, bool randomAccess);
+#ifdef PGXC
+extern Tuplesortstate *tuplesort_begin_merge(TupleDesc tupDesc,
+					 int nkeys, AttrNumber *attNums,
+					 Oid *sortOperators, bool *nullsFirstFlags,
+					 RemoteQueryState *combiner,
+					 int workMem);
+#endif
 
 extern void tuplesort_set_bound(Tuplesortstate *state, int64 bound);