Bug #28476: force index on a disabled myisam index gives error 124

When processing the USE/FORCE index hints
the optimizer was not checking if the indexes 
specified are enabled (see ALTER TABLE).
Fixed by:
 Backporting the fix for bug 20604 to 5.0


mysql-test/r/key.result:
  Test for BUG 20604.
  The important part of the test is the explain output that 
  tests what indexes are used.
mysql-test/r/myisam.result:
  Bug #28476: test cases
mysql-test/t/key.test:
  Bug 20604: 
  The minimal test case that reveals the bug. The optimizer for 
  aggregates relies on keys disabled with ALTER TABLE ... DISABLE KEYS
  not being in the set TABLE::keys_in_use_for_query.
  When the execution engine tries to use a disabled index, MyISAM
  returns an error.
mysql-test/t/myisam.test:
  Bug #28476: test cases
sql/sql_base.cc:
  Bug #28476: 
   - Ignore disabled indexes in USE/FORCE index
sql/sql_select.cc:
  Bug 20604 : The intersection operation between table->s->keys_in_use 
  and table->keys_in_use_for_query is no longer necessary.
  We can trust that the latter is a subset of the former.
sql/table.h:
  Bug 20604:
  Added comments to TABLE_SHARE::keys_in_use and
  TABLE::keys_in_use_for_query.

mysql-test/r/key.result

@@ -455,3 +455,11 @@ ORDER BY c.b, c.d
 a	b	c	d	e	f	g	h	i	j	a	b	c	d
 2	2	1	2004-11-30 12:00:00	1	0	0	0	0	0	2	3388000	-553000	NULL
 DROP TABLE t1, t2;
+CREATE TABLE t1( a TINYINT, KEY(a) ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES( 1 );
+ALTER TABLE t1 DISABLE KEYS;
+EXPLAIN SELECT MAX(a) FROM t1 FORCE INDEX(a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+DROP TABLE t1;
+End of 5.0 tests.

mysql-test/r/myisam.result

@@ -1780,4 +1780,30 @@ create table t3 (c1 int) engine=myisam pack_keys=default;
 create table t4 (c1 int) engine=myisam pack_keys=2;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '2' at line 1
 drop table t1, t2, t3;
+CREATE TABLE t1(a INT, b INT, KEY inx (a), UNIQUE KEY uinx (b)) ENGINE=MyISAM;
+INSERT INTO t1(a,b) VALUES (1,1),(2,2),(3,3),(4,4),(5,5);
+SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
+a
+1
+ALTER TABLE t1 DISABLE KEYS;
+SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
+a
+1
+SELECT a FROM t1 USE INDEX (inx) WHERE a=1;
+a
+1
+SELECT b FROM t1 FORCE INDEX (uinx) WHERE b=1;
+b
+1
+SELECT b FROM t1 USE INDEX (uinx) WHERE b=1;
+b
+1
+SELECT a FROM t1 FORCE INDEX (inx,uinx) WHERE a=1;
+a
+1
+ALTER TABLE t1 ENABLE KEYS;
+SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
+a
+1
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/key.test

@@ -432,3 +432,15 @@ ORDER BY c.b, c.d
 ;
 
 DROP TABLE t1, t2;
+
+
+#
+# Bug #20604: Test for disabled keys with aggregate functions and FORCE INDEX.
+#
+CREATE TABLE t1( a TINYINT, KEY(a) ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES( 1 );
+ALTER TABLE t1 DISABLE KEYS;
+EXPLAIN SELECT MAX(a) FROM t1 FORCE INDEX(a);
+DROP TABLE t1;
+
+--echo End of 5.0 tests.

mysql-test/t/myisam.test

@@ -1145,4 +1145,20 @@ create table t3 (c1 int) engine=myisam pack_keys=default;
 create table t4 (c1 int) engine=myisam pack_keys=2;
 drop table t1, t2, t3;
 
+#
+# Bug#28476: force index on a disabled myisam index gives error 124
+#
+CREATE TABLE t1(a INT, b INT, KEY inx (a), UNIQUE KEY uinx (b)) ENGINE=MyISAM;
+INSERT INTO t1(a,b) VALUES (1,1),(2,2),(3,3),(4,4),(5,5);
+SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
+ALTER TABLE t1 DISABLE KEYS;
+SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
+SELECT a FROM t1 USE INDEX (inx) WHERE a=1;
+SELECT b FROM t1 FORCE INDEX (uinx) WHERE b=1;
+SELECT b FROM t1 USE INDEX (uinx) WHERE b=1;
+SELECT a FROM t1 FORCE INDEX (inx,uinx) WHERE a=1;
+ALTER TABLE t1 ENABLE KEYS;
+SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
+DROP TABLE t1;
+
 --echo End of 5.0 tests

sql/sql_base.cc

@@ -4811,7 +4811,12 @@ bool setup_tables(THD *thd, Name_resolution_context *context,
       get_key_map_from_key_list(&map, table, table_list->use_index);
       if (map.is_set_all())
 	DBUG_RETURN(1);
-      table->keys_in_use_for_query=map;
+      /* 
+	 Don't introduce keys in keys_in_use_for_query that weren't there 
+	 before. FORCE/USE INDEX should not add keys, it should only remove
+	 all keys except the key(s) specified in the hint.
+      */
+      table->keys_in_use_for_query.intersect(map);
     }
     if (table_list->ignore_index)
     {

sql/sql_select.cc

@@ -12246,10 +12246,11 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
   LINT_INIT(ref_key_parts);
 
   /*
-    Check which keys can be used to resolve ORDER BY.
-    We must not try to use disabled keys.
+    Keys disabled by ALTER TABLE ... DISABLE KEYS should have already
+    been taken into account.
   */
-  usable_keys= table->s->keys_in_use;
+  usable_keys= table->keys_in_use_for_query;
+  DBUG_ASSERT(usable_keys.is_subset(table->s->keys_in_use));
 
   for (ORDER *tmp_order=order; tmp_order ; tmp_order=tmp_order->next)
   {

sql/table.h

@@ -137,7 +137,12 @@ typedef struct st_table_share
   const char *table_name;               /* Table name (for open) */
   const char *path;                     /* Path to .frm file (from datadir) */
   LEX_STRING connect_string;
-  key_map keys_in_use;                  /* Keys in use for table */
+
+  /* 
+     Set of keys in use, implemented as a Bitmap.
+     Excludes keys disabled by ALTER TABLE ... DISABLE KEYS.
+  */
+  key_map keys_in_use;
   key_map keys_for_keyread;
   ulong   avg_row_length;		/* create information */
   ulong   raid_chunksize;
@@ -206,7 +211,21 @@ struct st_table {
 
   byte *record[2];			/* Pointer to records */
   byte *insert_values;                  /* used by INSERT ... UPDATE */
-  key_map quick_keys, used_keys, keys_in_use_for_query;
+  key_map quick_keys, used_keys;
+
+  /*
+    A set of keys that can be used in the query that references this
+    table 
+
+    All indexes disabled on the table's TABLE_SHARE (see TABLE::s) will be 
+    subtracted from this set upon instantiation. Thus for any TABLE t it holds
+    that t.keys_in_use_for_query is a subset of t.s.keys_in_use. Generally we 
+    must not introduce any new keys here (see setup_tables).
+
+    The set is implemented as a bitmap.
+  */
+  key_map keys_in_use_for_query;
+  key_map merge_keys;
   KEY  *key_info;			/* data of keys in database */
 
   Field *next_number_field,		/* Set if next_number is activated */