Bug #31094: Forcing index-based sort doesn't work anymore if joins are done

A rule was introduced by the 5.1 part of the fix for bug 27531 to 
prefer filesort over indexed ORDER BY when accessing all of the rows of a 
table (because it's faster). This new rule was not accounting for the 
presence of a LIMIT clause.
Fixed the condition for this rule so it will prefer filesort over 
indexed ORDER BY only if no LIMIT.

mysql-test/r/compress.result

@@ -611,11 +611,11 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t3.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t3	index	period	period	4	NULL	1	
 1	SIMPLE	t1	ref	period	period	4	test.t3.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t1.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t1	index	period	period	4	NULL	1	
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 select period from t1;
 period

mysql-test/r/join.result

@@ -897,4 +897,168 @@ select '^^: The above should be ~= 20 + cost(select * from t1). Value less than
 Z
 ^^: The above should be ~= 20 + cost(select * from t1). Value less than 20 is an error
 drop table t1, t2;
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT);
+CREATE TABLE t2 (c INT PRIMARY KEY, d INT);
+INSERT INTO t1 VALUES(1,NULL),(2,NULL),(3,NULL),(4,NULL);
+INSERT INTO t1 SELECT a + 4, b FROM t1;
+INSERT INTO t1 SELECT a + 8, b FROM t1;
+INSERT INTO t1 SELECT a + 16, b FROM t1;
+INSERT INTO t1 SELECT a + 32, b FROM t1;
+INSERT INTO t1 SELECT a + 64, b FROM t1;
+INSERT INTO t2 SELECT a, b FROM t1;
+EXPLAIN SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a LIMIT 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	2	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.b	1	
+EXPLAIN SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a LIMIT 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	PRIMARY	PRIMARY	4	NULL	2	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	
+SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a LIMIT 2;
+a	b	c	d
+SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a LIMIT 2;
+a	b	c	d
+1	NULL	1	NULL
+2	NULL	2	NULL
+EXPLAIN SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	128	Using filesort
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.b	1	
+EXPLAIN SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	PRIMARY	NULL	NULL	NULL	128	Using filesort
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	
+SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a;
+a	b	c	d
+SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a;
+a	b	c	d
+1	NULL	1	NULL
+2	NULL	2	NULL
+3	NULL	3	NULL
+4	NULL	4	NULL
+5	NULL	5	NULL
+6	NULL	6	NULL
+7	NULL	7	NULL
+8	NULL	8	NULL
+9	NULL	9	NULL
+10	NULL	10	NULL
+11	NULL	11	NULL
+12	NULL	12	NULL
+13	NULL	13	NULL
+14	NULL	14	NULL
+15	NULL	15	NULL
+16	NULL	16	NULL
+17	NULL	17	NULL
+18	NULL	18	NULL
+19	NULL	19	NULL
+20	NULL	20	NULL
+21	NULL	21	NULL
+22	NULL	22	NULL
+23	NULL	23	NULL
+24	NULL	24	NULL
+25	NULL	25	NULL
+26	NULL	26	NULL
+27	NULL	27	NULL
+28	NULL	28	NULL
+29	NULL	29	NULL
+30	NULL	30	NULL
+31	NULL	31	NULL
+32	NULL	32	NULL
+33	NULL	33	NULL
+34	NULL	34	NULL
+35	NULL	35	NULL
+36	NULL	36	NULL
+37	NULL	37	NULL
+38	NULL	38	NULL
+39	NULL	39	NULL
+40	NULL	40	NULL
+41	NULL	41	NULL
+42	NULL	42	NULL
+43	NULL	43	NULL
+44	NULL	44	NULL
+45	NULL	45	NULL
+46	NULL	46	NULL
+47	NULL	47	NULL
+48	NULL	48	NULL
+49	NULL	49	NULL
+50	NULL	50	NULL
+51	NULL	51	NULL
+52	NULL	52	NULL
+53	NULL	53	NULL
+54	NULL	54	NULL
+55	NULL	55	NULL
+56	NULL	56	NULL
+57	NULL	57	NULL
+58	NULL	58	NULL
+59	NULL	59	NULL
+60	NULL	60	NULL
+61	NULL	61	NULL
+62	NULL	62	NULL
+63	NULL	63	NULL
+64	NULL	64	NULL
+65	NULL	65	NULL
+66	NULL	66	NULL
+67	NULL	67	NULL
+68	NULL	68	NULL
+69	NULL	69	NULL
+70	NULL	70	NULL
+71	NULL	71	NULL
+72	NULL	72	NULL
+73	NULL	73	NULL
+74	NULL	74	NULL
+75	NULL	75	NULL
+76	NULL	76	NULL
+77	NULL	77	NULL
+78	NULL	78	NULL
+79	NULL	79	NULL
+80	NULL	80	NULL
+81	NULL	81	NULL
+82	NULL	82	NULL
+83	NULL	83	NULL
+84	NULL	84	NULL
+85	NULL	85	NULL
+86	NULL	86	NULL
+87	NULL	87	NULL
+88	NULL	88	NULL
+89	NULL	89	NULL
+90	NULL	90	NULL
+91	NULL	91	NULL
+92	NULL	92	NULL
+93	NULL	93	NULL
+94	NULL	94	NULL
+95	NULL	95	NULL
+96	NULL	96	NULL
+97	NULL	97	NULL
+98	NULL	98	NULL
+99	NULL	99	NULL
+100	NULL	100	NULL
+101	NULL	101	NULL
+102	NULL	102	NULL
+103	NULL	103	NULL
+104	NULL	104	NULL
+105	NULL	105	NULL
+106	NULL	106	NULL
+107	NULL	107	NULL
+108	NULL	108	NULL
+109	NULL	109	NULL
+110	NULL	110	NULL
+111	NULL	111	NULL
+112	NULL	112	NULL
+113	NULL	113	NULL
+114	NULL	114	NULL
+115	NULL	115	NULL
+116	NULL	116	NULL
+117	NULL	117	NULL
+118	NULL	118	NULL
+119	NULL	119	NULL
+120	NULL	120	NULL
+121	NULL	121	NULL
+122	NULL	122	NULL
+123	NULL	123	NULL
+124	NULL	124	NULL
+125	NULL	125	NULL
+126	NULL	126	NULL
+127	NULL	127	NULL
+128	NULL	128	NULL
+DROP TABLE IF EXISTS t1,t2;
 End of 5.0 tests.

mysql-test/r/select.result

@@ -607,11 +607,11 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t3.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t3	index	period	period	4	NULL	1	
 1	SIMPLE	t1	ref	period	period	4	test.t3.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t1.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t1	index	period	period	4	NULL	1	
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 select period from t1;
 period

mysql-test/r/ssl.result

@@ -608,11 +608,11 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t3.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t3	index	period	period	4	NULL	1	
 1	SIMPLE	t1	ref	period	period	4	test.t3.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t1.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t1	index	period	period	4	NULL	1	
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 select period from t1;
 period

mysql-test/r/ssl_compress.result

@@ -611,11 +611,11 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t3.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t3	index	period	period	4	NULL	1	
 1	SIMPLE	t1	ref	period	period	4	test.t3.period	4181	
 explain select * from t3 as t1,t3 where t1.period=t3.period order by t1.period limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	period	NULL	NULL	NULL	41810	Using filesort
+1	SIMPLE	t1	index	period	period	4	NULL	1	
 1	SIMPLE	t3	ref	period	period	4	test.t1.period	4181	
 select period from t1;
 period

mysql-test/t/join.test

@@ -698,4 +698,33 @@ select '^^: The above should be ~= 20 + cost(select * from t1). Value less than
 
 drop table t1, t2;
 
+#
+# Bug #31094: Forcing index-based sort doesn't work anymore if joins are
+# done
+#
+
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT);
+CREATE TABLE t2 (c INT PRIMARY KEY, d INT);
+
+INSERT INTO t1 VALUES(1,NULL),(2,NULL),(3,NULL),(4,NULL);
+INSERT INTO t1 SELECT a + 4, b FROM t1;
+INSERT INTO t1 SELECT a + 8, b FROM t1;
+INSERT INTO t1 SELECT a + 16, b FROM t1;
+INSERT INTO t1 SELECT a + 32, b FROM t1;
+INSERT INTO t1 SELECT a + 64, b FROM t1;
+INSERT INTO t2 SELECT a, b FROM t1;
+
+#expect indexed ORDER BY
+EXPLAIN SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a LIMIT 2;
+EXPLAIN SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a LIMIT 2;
+SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a LIMIT 2;
+SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a LIMIT 2;
+
+#expect filesort
+EXPLAIN SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a;
+EXPLAIN SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a;
+SELECT * FROM t1 JOIN t2 ON b=c ORDER BY a;
+SELECT * FROM t1 JOIN t2 ON a=c ORDER BY a;
+
+DROP TABLE IF EXISTS t1,t2;
 --echo End of 5.0 tests.

sql/sql_select.cc

@@ -12775,12 +12775,6 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
     LINT_INIT(best_key_direction);
     LINT_INIT(best_records); 
 
-    /* 
-      filesort() and join cache are usually faster than reading in 
-      index order and not using join cache
-    */
-    if (tab->type == JT_ALL && tab->join->tables > tab->join->const_tables + 1)
-      DBUG_RETURN(0);
     /*
       If not used with LIMIT, only use keys if the whole query can be
       resolved with a key;  This is because filesort() is usually faster than
@@ -12788,6 +12782,12 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
     */
     if (select_limit >= table_records)
     {
+      /* 
+        filesort() and join cache are usually faster than reading in 
+        index order and not using join cache
+        */
+      if (tab->type == JT_ALL && tab->join->tables > tab->join->const_tables + 1)
+        DBUG_RETURN(0);
       keys= *table->file->keys_to_use_for_scanning();
       keys.merge(table->covering_keys);