Fix for BUG#9213: GROUP BY returns wrong query results:

Make test_if_skip_sort_order() rebuild tab->ref if it decides to use an index
different from the index join optimizer has choosen.  


mysql-test/r/group_by.result:
  Testcase for BUG#9213
mysql-test/t/group_by.test:
  Testcase for BUG#9213
sql/table.h:
  Added comments about TABLE::used_keys

1 files changed, 25 insertions, 0 deletions

diff --git a/mysql-test/t/group_by.test b/mysql-test/t/group_by.test
index afd479c520e..327be1b724b 100644
--- a/mysql-test/t/group_by.test
+++ b/mysql-test/t/group_by.test
@@ -489,3 +489,28 @@ select a,sum(b) from t1 where a=1 group by c having a=1;
 select a as d,sum(b) from t1 where a=1 group by c having d=1;
 select sum(a)*sum(b) as d from t1 where a=1 group by c having d > 0;
 drop table t1;
+
+# Test for BUG#9213 GROUP BY query on utf-8 key returns wrong results
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(8),(9);
+create table t2 (
+  a int,
+  b varchar(200) NOT NULL,
+  c varchar(50) NOT NULL,
+  d varchar(100) NOT NULL,
+  primary key (a,b(132),c,d),
+  key a (a,b)
+) charset=utf8;
+
+insert into t2 select 
+   x3.a,  -- 3
+   concat('val-', x3.a + 3*x4.a), -- 12
+   concat('val-', @a:=x3.a + 3*x4.a + 12*C.a), -- 120
+   concat('val-', @a + 120*D.a)
+from t1 x3, t1 x4, t1 C, t1 D where x3.a < 3 and x4.a < 4 and D.a < 4;
+delete from t2  where a = 2 and b = 'val-2' limit 30;
+
+explain select c from t2 where a = 2 and b = 'val-2' group by c;
+select c from t2 where a = 2 and b = 'val-2' group by c;
+drop table t1,t2;
+