Backport into build-200909221805-5.1.37sp1

> ------------------------------------------------------------
> revno: 3059 [merge]
> revision-id: martin.hansson@sun.com-20090810140851-aw5peehzdxi4gjja
> parent: iggy@mysql.com-20090806145453-ion37sfdsldwwjrj
> parent: martin.hansson@sun.com-20090807115140-7fn6wjx0mrui7zl5
> committer: Martin Hansson <martin.hansson@sun.com>
> branch nick: 5.1bt
> timestamp: Mon 2009-08-10 16:08:51 +0200
> message:
>   Merge
> ------------------------------------------------------------
> Use --include-merges or -n0 to see merged revisions.

mysql-test/r/order_by.result

@@ -1500,3 +1500,60 @@ id1
 15
 16
 DROP TABLE t1;
+CREATE TABLE t1 (
+a INT,
+b INT NOT NULL,
+c char(100),
+KEY (b, c),
+KEY (b, a, c)
+)
+DEFAULT CHARSET = utf8;
+INSERT INTO t1 VALUES 
+(1,  1, 1),
+(2,  2, 2),
+(3,  3, 3),
+(4,  4, 4),
+(5,  5, 5),
+(6,  6, 6),
+(7,  7, 7),
+(8,  8, 8),
+(9,  9, 9);
+INSERT INTO t1 SELECT a + 10,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 20,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 40,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 80,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 160, b, c FROM t1;
+INSERT INTO t1 SELECT a + 320, b, c FROM t1;
+INSERT INTO t1 SELECT a + 640, b, c FROM t1;
+INSERT INTO t1 SELECT a + 1280, b, c FROM t1 LIMIT 80;
+EXPLAIN
+SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	b,b_2	b	4	NULL	226	Using where
+SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
+a
+2071
+2061
+2051
+2041
+2031
+2021
+2011
+2001
+1991
+EXPLAIN
+SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	b,b_2	b	4	NULL	226	Using where; Using temporary
+SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
+a
+2071
+2061
+2051
+2041
+2031
+2021
+2011
+2001
+1991
+DROP TABLE t1;

mysql-test/t/order_by.test

@@ -1361,3 +1361,44 @@ DROP TABLE t1;
 
 
 
+#
+# Bug#46454: MySQL wrong index optimisation leads to incorrect result & crashes 
+#
+CREATE TABLE t1 (
+  a INT,
+  b INT NOT NULL,
+  c char(100),
+  KEY (b, c),
+  KEY (b, a, c)
+)
+DEFAULT CHARSET = utf8;
+
+INSERT INTO t1 VALUES 
+(1,  1, 1),
+(2,  2, 2),
+(3,  3, 3),
+(4,  4, 4),
+(5,  5, 5),
+(6,  6, 6),
+(7,  7, 7),
+(8,  8, 8),
+(9,  9, 9);
+
+INSERT INTO t1 SELECT a + 10,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 20,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 40,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 80,  b, c FROM t1;
+INSERT INTO t1 SELECT a + 160, b, c FROM t1;
+INSERT INTO t1 SELECT a + 320, b, c FROM t1;
+INSERT INTO t1 SELECT a + 640, b, c FROM t1;
+INSERT INTO t1 SELECT a + 1280, b, c FROM t1 LIMIT 80;
+
+EXPLAIN
+SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
+SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
+
+EXPLAIN
+SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
+SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
+
+DROP TABLE t1;

sql/sql_select.cc

@@ -6141,7 +6141,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
         }
 
       }
-      if (tmp || !cond)
+      if (tmp || !cond || tab->type == JT_REF)
       {
         DBUG_EXECUTE("where",print_where(tmp,tab->table->alias, QT_ORDINARY););
 	SQL_SELECT *sel= tab->select= ((SQL_SELECT*)
@@ -6155,7 +6155,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
           The guard will turn the predicate on only after
           the first match for outer tables is encountered.
 	*/        
-        if (cond)
+        if (cond && tmp)
         {
           /*
             Because of QUICK_GROUP_MIN_MAX_SELECT there may be a select without
@@ -12931,6 +12931,8 @@ find_field_in_item_list (Field *field, void *data)
 
   The index must cover all fields in <order>, or it will not be considered.
 
+  @param no_changes No changes will be made to the query plan.
+
   @todo
     - sergeyp: Results of all index merge selects actually are ordered 
     by clustered PK values.
@@ -13265,6 +13267,15 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
       }
       if (!no_changes)
       {
+        /* 
+           If ref_key used index tree reading only ('Using index' in EXPLAIN),
+           and best_key doesn't, then revert the decision.
+        */
+        if (!table->covering_keys.is_set(best_key) && table->key_read)
+        {
+          table->key_read= 0;
+          table->file->extra(HA_EXTRA_NO_KEYREAD);          
+        }        
         if (!quick_created)
 	{
           tab->index= best_key;
@@ -13281,16 +13292,6 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
             table->key_read=1;
             table->file->extra(HA_EXTRA_KEYREAD);
           }
-          else if (table->key_read)
-          {
-            /*
-              Clear the covering key read flags that might have been
-              previously set for some key other than the current best_key.
-            */
-            table->key_read= 0;
-            table->file->extra(HA_EXTRA_NO_KEYREAD);
-          }
-
           table->file->ha_index_or_rnd_end();
           if (join->select_options & SELECT_DESCRIBE)
           {

sql/table.h

@@ -753,7 +753,13 @@ struct st_table {
   */
   my_bool force_index;
   my_bool distinct,const_table,no_rows;
-  my_bool key_read, no_keyread;
+
+  /**
+     If set, the optimizer has found that row retrieval should access index 
+     tree only.
+   */
+  my_bool key_read;
+  my_bool no_keyread;
   /*
     Placeholder for an open table which prevents other connections
     from taking name-locks on this table. Typically used with