Fix for BUG#13455: Make "ref" optimizer able to make this inference:

"t.key BETWEEN c1 AND c2" and c1 = c2 -> can access table t using "t.key = c1".

mysql-test/r/heap.result

@@ -379,10 +379,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	v	NULL	NULL	NULL	271	Using where
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	v	NULL	NULL	NULL	271	Using where
+1	SIMPLE	t1	ref	v	v	13	const	10	Using where
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	v	NULL	NULL	NULL	271	Using where
+1	SIMPLE	t1	ref	v	v	13	const	10	Using where
 alter table t1 add unique(v);
 ERROR 23000: Duplicate entry '{ ' for key 1
 select concat('*',v,'*',c,'*',t,'*') as qq from t1 where v='a' order by length(concat('*',v,'*',c,'*',t,'*'));
@@ -602,10 +602,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	13	NULL	#	Using where
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	13	NULL	#	Using where
+1	SIMPLE	t1	ref	v	v	13	const	#	Using where
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	13	NULL	#	Using where
+1	SIMPLE	t1	ref	v	v	13	const	#	Using where
 alter table t1 add unique(v);
 ERROR 23000: Duplicate entry '{ ' for key 1
 select concat('*',v,'*',c,'*',t,'*') as qq from t1 where v='a' order by length(concat('*',v,'*',c,'*',t,'*'));

mysql-test/r/innodb.result

@@ -1997,10 +1997,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	13	NULL	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	13	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	13	const	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	13	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	13	const	#	Using where; Using index
 alter table t1 add unique(v);
 ERROR 23000: Duplicate entry '{ ' for key 1
 alter table t1 add key(v);
@@ -2188,10 +2188,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	303	NULL	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	303	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	303	const	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	303	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	303	const	#	Using where; Using index
 explain select * from t1 where v='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	v	v	303	const	#	Using where
@@ -2268,10 +2268,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	33	NULL	#	Using where
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	33	NULL	#	Using where
+1	SIMPLE	t1	ref	v	v	33	const	#	Using where
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	33	NULL	#	Using where
+1	SIMPLE	t1	ref	v	v	33	const	#	Using where
 explain select * from t1 where v='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	v	v	33	const	#	Using where

mysql-test/r/myisam.result

@@ -802,10 +802,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	13	NULL	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	13	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	13	const	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	13	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	13	const	#	Using where; Using index
 alter table t1 add unique(v);
 ERROR 23000: Duplicate entry '{ ' for key 1
 alter table t1 add key(v);
@@ -993,10 +993,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	303	NULL	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	303	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	303	const	#	Using where; Using index
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	303	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	v	v	303	const	#	Using where; Using index
 explain select * from t1 where v='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	v	v	303	const	#	Using where
@@ -1073,10 +1073,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	33	NULL	#	Using where
 explain select count(*) from t1 where v between 'a' and 'a ';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	33	NULL	#	Using where
+1	SIMPLE	t1	ref	v	v	33	const	#	Using where
 explain select count(*) from t1 where v between 'a' and 'a ' and v between 'a  ' and 'b\n';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	v	v	33	NULL	#	Using where
+1	SIMPLE	t1	ref	v	v	33	const	#	Using where
 explain select * from t1 where v='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	v	v	33	const	#	Using where

mysql-test/r/range.result

@@ -1,4 +1,4 @@
-drop table if exists t1, t2;
+drop table if exists t1, t2, t3;
 CREATE TABLE t1 (
 event_date date DEFAULT '0000-00-00' NOT NULL,
 type int(11) DEFAULT '0' NOT NULL,
@@ -787,3 +787,26 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	range	PRIMARY	PRIMARY	8	NULL	#	Using where; Using index
 drop view v1;
 drop table t1;
+create table t3 (a int);
+insert into t3 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t1 (a varchar(10), filler char(200), key(a)) charset=binary;
+insert into t1 values ('a','');
+insert into t1 values ('a ','');
+insert into t1 values ('a  ', '');
+insert into t1 select concat('a', 1000 + A.a + 10 * (B.a + 10 * C.a)), ''
+  from t3 A, t3 B, t3 C;
+create table t2 (a varchar(10), filler char(200), key(a));
+insert into t2 select * from t1;
+explain select * from t1 where a between 'a' and 'a ';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	a	a	13	NULL	#	Using where
+explain select * from t1 where a = 'a' or a='a ';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	a	a	13	NULL	#	Using where
+explain select * from t2 where a between 'a' and 'a ';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ref	a	a	13	const	#	Using where
+explain select * from t2 where a = 'a' or a='a ';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ref	a	a	13	const	#	Using where
+drop table t1,t2,t3;

mysql-test/t/range.test

@@ -3,7 +3,7 @@
 #
 
 --disable_warnings
-drop table if exists t1, t2;
+drop table if exists t1, t2, t3;
 --enable_warnings
 
 CREATE TABLE t1 (
@@ -600,3 +600,29 @@ explain select * from v1 where a between 3 and 4 and b between 1 and 2;
  
 drop view v1;
 drop table t1;
+
+# BUG#13455: 
+create table t3 (a int);
+insert into t3 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+create table t1 (a varchar(10), filler char(200), key(a)) charset=binary;
+insert into t1 values ('a','');
+insert into t1 values ('a ','');
+insert into t1 values ('a  ', '');
+insert into t1 select concat('a', 1000 + A.a + 10 * (B.a + 10 * C.a)), ''
+  from t3 A, t3 B, t3 C;
+
+create table t2 (a varchar(10), filler char(200), key(a));
+insert into t2 select * from t1;
+
+--replace_column 9 #
+explain select * from t1 where a between 'a' and 'a '; 
+--replace_column 9 #
+explain select * from t1 where a = 'a' or a='a ';
+
+--replace_column 9 #
+explain select * from t2 where a between 'a' and 'a '; 
+--replace_column 9 #
+explain select * from t2 where a = 'a' or a='a ';
+
+drop table t1,t2,t3;

sql/sql_select.cc

@@ -2409,6 +2409,7 @@ add_key_field(KEY_FIELD **key_fields,uint and_level, Item_func *cond,
         !field->table->maybe_null || field->null_ptr)
       return;					// Not a key. Skip it
     exists_optimize= KEY_OPTIMIZE_EXISTS;
+    DBUG_ASSERT(num_values == 1);
   }
   else
   {
@@ -2460,7 +2461,26 @@ add_key_field(KEY_FIELD **key_fields,uint and_level, Item_func *cond,
         eq_func is NEVER true when num_values > 1
        */
       if (!eq_func)
+      {
+        /* 
+          Additional optimization: if we're processing
+          "t.key BETWEEN c1 AND c1" then proceed as if we were processing
+          "t.key = c1".
+          TODO: This is a very limited fix. A more generic fix is possible. 
+          There are 2 options:
+          A) Make equality propagation code be able to handle BETWEEN
+             (including cases like t1.key BETWEEN t2.key AND t3.key)
+          B) Make range optimizer to infer additional "t.key = c" equalities
+             and use them in equality propagation process (see details in
+             OptimizerKBAndTodo)
+        */
+        if ((cond->functype() == Item_func::BETWEEN) && 
+             value[0]->eq(value[1], field->binary()))
+          eq_func= TRUE;
+        else
           return;
+      }
+
       if (field->result_type() == STRING_RESULT)
       {
         if ((*value)->result_type() != STRING_RESULT)
@@ -2487,7 +2507,6 @@ add_key_field(KEY_FIELD **key_fields,uint and_level, Item_func *cond,
       }
     }
   }
-  DBUG_ASSERT(num_values == 1);
   /*
     For the moment eq_func is always true. This slot is reserved for future
     extensions where we want to remembers other things than just eq comparisons