Fix for bug #34928: Confusion by having Primary Key and Index

The bug is a regression introduced in 5.1 by the patch for bug28404.

Under some circumstances test_if_skip_sort_order() could leave some
data structures in an inconsistent state so that some parts of code
could assume the selected execution strategy for GROUP BY/DISTINCT as
a loose index scan (e.g. JOIN_TAB::is_using_loose_index_scan()), while
the actual strategy chosen was an ordered index scan, which led to
wrong data being returned.

Fixed test_if_skip_sort_order() so that when changing the type for a
join table, select->quick is reset not only for EXPLAIN, but for the 
actual join execution as well, to not confuse code that depends on its
value to determine the chosen GROUP BY/DISTINCT strategy.

1 files changed, 23 insertions, 0 deletions

diff --git a/mysql-test/r/distinct.result b/mysql-test/r/distinct.result
index b2a9eb04c04..15e4c3f15b3 100644
--- a/mysql-test/r/distinct.result
+++ b/mysql-test/r/distinct.result
@@ -682,3 +682,26 @@ a	a	b
 1	1	3
 DROP TABLE t1;
 End of 5.0 tests
+CREATE TABLE t1(a INT, b INT, c INT, d INT, e INT,
+PRIMARY KEY(a,b,c,d,e),
+KEY(a,b,d,c)
+);
+INSERT INTO t1(a, b, c) VALUES (1, 1, 1),
+(1, 1, 2),
+(1, 1, 3),
+(1, 2, 1),
+(1, 2, 2),
+(1, 2, 3);
+EXPLAIN SELECT DISTINCT a, b, d, c FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	a	16	NULL	6	Using index
+SELECT DISTINCT a, b, d, c FROM t1;
+a	b	d	c
+1	1	0	1
+1	1	0	2
+1	1	0	3
+1	2	0	1
+1	2	0	2
+1	2	0	3
+DROP TABLE t1;
+End of 5.1 tests