Bug#44821: select distinct on partitioned table returns wrong results

Range analysis did not request sorted output from the storage engine,
which cause partitioned handlers to process one partition at a time
while reading key prefixes in ascending order, causing values to be 
missed. Fixed by always requesting sorted order during range analysis.
This fix is introduced in 6.0 by the fix for bug no 41136.

mysql-test/r/group_min_max.result:
  Bug#44821: Test result.
mysql-test/t/group_min_max.test:
  Bug#44821: Test case
sql/opt_range.cc:
  Bug#44821: Fix.

mysql-test/r/group_min_max.result

@@ -2463,3 +2463,61 @@ c
 2
 DROP TABLE t1;
 End of 5.0 tests
+CREATE TABLE t1 ( a INT, b INT, c INT, KEY bc(b, c) )
+PARTITION BY KEY (a, b) PARTITIONS 3
+;
+INSERT INTO t1 VALUES
+(17, 1, -8),
+(3,  1, -7),
+(23, 1, -6),
+(22, 1, -5),
+(11, 1, -4),
+(21, 1, -3),
+(19, 1, -2),
+(30, 1, -1),
+(20, 1, 1),
+(16, 1, 2),
+(18, 1, 3),
+(9,  1, 4),
+(15, 1, 5),
+(28, 1, 6),
+(29, 1, 7),
+(25, 1, 8),
+(10, 1, 9),
+(13, 1, 10),
+(27, 1, 11),
+(24, 1, 12),
+(12, 1, 13),
+(26, 1, 14),
+(14, 1, 15)
+;
+SELECT b, c FROM t1 WHERE b = 1 GROUP BY b, c;
+b	c
+1	-8
+1	-7
+1	-6
+1	-5
+1	-4
+1	-3
+1	-2
+1	-1
+1	1
+1	2
+1	3
+1	4
+1	5
+1	6
+1	7
+1	8
+1	9
+1	10
+1	11
+1	12
+1	13
+1	14
+1	15
+EXPLAIN
+SELECT b, c FROM t1 WHERE b = 1 GROUP BY b, c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	bc	bc	10	NULL	7	Using where; Using index for group-by
+DROP TABLE t1;

mysql-test/t/group_min_max.test

@@ -983,3 +983,43 @@ SELECT DISTINCT c FROM t1 WHERE d=4;
 DROP TABLE t1;
 
 --echo End of 5.0 tests
+#
+# Bug#44821: select distinct on partitioned table returns wrong results
+#
+CREATE TABLE t1 ( a INT, b INT, c INT, KEY bc(b, c) )
+PARTITION BY KEY (a, b) PARTITIONS 3
+;
+
+INSERT INTO t1 VALUES
+(17, 1, -8),
+(3,  1, -7),
+(23, 1, -6),
+(22, 1, -5),
+(11, 1, -4),
+(21, 1, -3),
+(19, 1, -2),
+(30, 1, -1),
+
+(20, 1, 1),
+(16, 1, 2),
+(18, 1, 3),
+(9,  1, 4),
+(15, 1, 5),
+(28, 1, 6),
+(29, 1, 7),
+(25, 1, 8),
+(10, 1, 9),
+(13, 1, 10),
+(27, 1, 11),
+(24, 1, 12),
+(12, 1, 13),
+(26, 1, 14),
+(14, 1, 15)
+;
+
+SELECT b, c FROM t1 WHERE b = 1 GROUP BY b, c;
+
+EXPLAIN
+SELECT b, c FROM t1 WHERE b = 1 GROUP BY b, c;
+
+DROP TABLE t1;

sql/opt_range.cc

@@ -8556,7 +8556,7 @@ int QUICK_RANGE_SELECT::get_next_prefix(uint prefix_length,
     result= file->read_range_first(last_range->min_keypart_map ? &start_key : 0,
 				   last_range->max_keypart_map ? &end_key : 0,
                                    test(last_range->flag & EQ_RANGE),
-				   sorted);
+				   TRUE);
     if (last_range->flag == (UNIQUE_RANGE | EQ_RANGE))
       last_range= 0;			// Stop searching