Bug #33061: ORDER BY DESC becomes ASC in NDB partition pruning to one partition

When partition pruning resulted in an ordered index scan spanning only
one partition, any descending flag for the scan was wrongly discarded,
turning ORDER BY DESC into ORDER BY ASC, and similar problems.

Fixed by correctly passing descending flag in SCAN_TABREQ signal sent
to data nodes.

mysql-test/suite/ndb/r/ndb_partition_key.result

@@ -38,6 +38,23 @@ a	b	c
 1	10	3
 1	11	3
 1	12	3
+select max(b) from t1 where a = 1;
+max(b)
+12
+select b from t1 where a = 1 order by b desc;
+b
+12
+11
+10
+9
+8
+7
+6
+5
+4
+3
+2
+1
 DROP TABLE t1;
 CREATE TABLE t1 (a INT, b CHAR(10) COLLATE latin1_bin, c INT, d INT,
 PRIMARY KEY (a,b,c) USING HASH)

mysql-test/suite/ndb/r/ndb_partition_range.result

@@ -46,6 +46,14 @@ a	b	c
 1	1	1
 6	1	1
 10	1	1
+INSERT into t1 values (1, 2, 2);
+select max(b) from t1 where a = 1;
+max(b)
+2
+select b from t1 where a = 1 order by b desc;
+b
+2
+1
 drop table t1;
 CREATE TABLE t1 (
 a int not null,

mysql-test/suite/ndb/t/ndb_partition_key.test

@@ -38,6 +38,10 @@ insert into t1 values
 
 select * from t1 order by b;
 
+# BUG#33061: ORDER BY DESC becomes ASC in NDB partition pruning to one partition
+select max(b) from t1 where a = 1;
+select b from t1 where a = 1 order by b desc;
+
 DROP TABLE t1;
 
 #

mysql-test/suite/ndb/t/ndb_partition_range.test

@@ -48,6 +48,11 @@ select * from t1 where a=21 order by a;
 select * from t1 where a in (1,6,10,21) order by a;
 select * from t1 where b=1 and a in (1,6,10,21) order by a;
 
+# BUG#33061: ORDER BY DESC becomes ASC in NDB partition pruning to one partition
+INSERT into t1 values (1, 2, 2);
+select max(b) from t1 where a = 1;
+select b from t1 where a = 1 order by b desc;
+
 drop table t1;
 
 #

storage/ndb/src/ndbapi/NdbScanOperation.cpp

@@ -1340,13 +1340,24 @@ NdbIndexScanOperation::readTuples(LockMode lm,
     if(insertATTRINFO(word) == -1)
       res = -1;
   }
-  if(!res && order_by){
-    m_ordered = true;
+  if (!res)
+  {
+    /**
+     * Note that it is valid to have order_desc true and order_by false.
+     *
+     * This means that there will be no merge sort among partitions, but
+     * each partition will still be returned in descending sort order.
+     *
+     * This is useful eg. if it is known that the scan spans only one
+     * partition.
+     */
     if (order_desc) {
       m_descending = true;
       ScanTabReq * req = CAST_PTR(ScanTabReq, theSCAN_TABREQ->getDataPtrSend());
       ScanTabReq::setDescendingFlag(req->requestInfo, true);
     }
+    if (order_by) {
+      m_ordered = true;
       Uint32 cnt = m_accessTable->getNoOfColumns() - 1;
       m_sort_columns = cnt; // -1 for NDB$NODE
       m_current_api_receiver = m_sent_receivers_count;
@@ -1365,6 +1376,7 @@ NdbIndexScanOperation::readTuples(LockMode lm,
 #endif
       }
     }
+  }
   m_this_bound_start = 0;
   m_first_bound_word = theKEYINFOptr;