Fixed LP bug #884175.

If in the where clause of the a query some comparison conditions on the
field under a MIN/MAX aggregate function contained constants whose sizes
exceeded the size of the field then the query could return a wrong result
when the optimizer had chosen to apply the MIN/MAX optimization.
With such conditions the MIN/MAX optimization still could be applied, yet
it would require a more thorough analysis of the keys built to find
the value of MIN/MAX aggregate functions with index look-ups.   
The current patch just prohibits using the MIN/MAX optimization in this
situation.

mysql-test/r/func_group.result

@@ -1828,4 +1828,51 @@ NULL
 NULL
 DROP TABLE t1,t2,t3;
 #
+# Bug #884175: MIN/MAX for short varchar = long const  
+#
+CREATE TABLE t1 (f1 varchar(1), f2 varchar(1), KEY (f2));
+INSERT INTO t1 VALUES ('b', 'b'), ('a','a');
+EXPLAIN 
+SELECT MAX(f1) FROM t1 WHERE f1 = 'abc';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT MAX(f1) FROM t1 WHERE f1 = 'abc';
+MAX(f1)
+NULL
+EXPLAIN
+SELECT MAX(f2) FROM t1 WHERE f2 = 'abc';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	f2	f2	4	const	1	Using where; Using index
+SELECT MAX(f2) FROM t1 WHERE f2 = 'abc';
+MAX(f2)
+NULL
+EXPLAIN
+SELECT MIN(f1) FROM t1 WHERE f1 >= 'abc';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT MIN(f1) FROM t1 WHERE f1 >= 'abc';
+MIN(f1)
+b
+EXPLAIN
+SELECT MIN(f2) FROM t1 WHERE f2 >= 'abc';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	f2	f2	4	NULL	2	Using where; Using index
+SELECT MIN(f2) FROM t1 WHERE f2 >= 'abc';
+MIN(f2)
+b
+EXPLAIN
+SELECT MIN(f1) FROM t1 WHERE f1 BETWEEN 'abc' AND 'b' ;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT MIN(f1) FROM t1 WHERE f1 BETWEEN 'abc' AND 'b' ;
+MIN(f1)
+b
+EXPLAIN
+SELECT MIN(f2) FROM t1 WHERE f2 BETWEEN 'abc' AND 'b' ;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	f2	f2	4	NULL	2	Using where; Using index
+SELECT MIN(f2) FROM t1 WHERE f2 BETWEEN 'abc' AND 'b' ;
+MIN(f2)
+b
+DROP TABLE t1;
 End of 5.2 tests

mysql-test/t/func_group.test

@@ -1194,4 +1194,37 @@ SELECT (SELECT MIN(t1.a) FROM t1,t2 WHERE t2.a = t3.b) FROM t3;
 DROP TABLE t1,t2,t3;
 
 --echo #
+--echo # Bug #884175: MIN/MAX for short varchar = long const  
+--echo #
+
+CREATE TABLE t1 (f1 varchar(1), f2 varchar(1), KEY (f2));
+INSERT INTO t1 VALUES ('b', 'b'), ('a','a');
+
+EXPLAIN 
+SELECT MAX(f1) FROM t1 WHERE f1 = 'abc';
+SELECT MAX(f1) FROM t1 WHERE f1 = 'abc';
+
+EXPLAIN
+SELECT MAX(f2) FROM t1 WHERE f2 = 'abc';
+SELECT MAX(f2) FROM t1 WHERE f2 = 'abc';
+
+EXPLAIN
+SELECT MIN(f1) FROM t1 WHERE f1 >= 'abc';
+SELECT MIN(f1) FROM t1 WHERE f1 >= 'abc';
+
+EXPLAIN
+SELECT MIN(f2) FROM t1 WHERE f2 >= 'abc';
+SELECT MIN(f2) FROM t1 WHERE f2 >= 'abc';
+
+EXPLAIN
+SELECT MIN(f1) FROM t1 WHERE f1 BETWEEN 'abc' AND 'b' ;
+SELECT MIN(f1) FROM t1 WHERE f1 BETWEEN 'abc' AND 'b' ;
+
+EXPLAIN
+SELECT MIN(f2) FROM t1 WHERE f2 BETWEEN 'abc' AND 'b' ;
+SELECT MIN(f2) FROM t1 WHERE f2 BETWEEN 'abc' AND 'b' ;
+
+DROP TABLE t1;
+
+
 --echo End of 5.2 tests

sql/opt_sum.cc

@@ -469,8 +469,8 @@ int opt_sum_query(THD *thd,
                           'const op field'
 
   @retval
-    0        func_item is a simple predicate: a field is compared with
-    constants
+    0      func_item is a simple predicate: a field is compared with a constant
+           whose length does not exceed the max length of the field values  
   @retval
     1        Otherwise
 */
@@ -490,6 +490,8 @@ bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
         return 0;
       if (!(args[1]= item_equal->get_const()))
         return 0;
+      if (args[0]->max_length < args[1]->max_length)
+        return 0;
     }
     break;
   case 1:
@@ -521,6 +523,8 @@ bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
     }
     else
       return 0;
+    if (args[0]->max_length < args[1]->max_length)
+      return 0;
     break;
   case 3:
     /* field BETWEEN const AND const */
@@ -534,6 +538,8 @@ bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
         if (!item->const_item())
           return 0;
         args[i]= item;
+        if (args[0]->max_length < args[i]->max_length)
+          return 0;
       }
     }
     else