Fix for BUG#11185.

The source of the problem is in Field_longlong::cmp. If 'this' is
an unsigned number, the method casts both the current value, and
the constant that we compare with to an unsigned number. As a
result if the constant we compare with is a negative number, it
wraps to some unsigned number, and the comparison is incorrect.

When the optimizer chooses the "range" access method, this problem
causes handler::read_range_next to reject the current key when the
upper bound key is a negative number because handler::compare_key
incorrectly considers the positive and negative keys to be equal.

The current patch does not correct the source of the problem in
Field_longlong::cmp because it is not easy to propagate sign
information about the constant at query execution time. Instead
the patch changes the range optimizer so that it never compares
unsiged fields with negative constants. As an added benefit,
queries that do such comparisons will execute faster because
the range optimizer replaces conditions like:
(a) (unsigned_int [< | <=] negative_constant) == FALSE
(b) (unsigned_int [> | >=] negative_constant) == TRUE
with the corresponding constants.
In some cases this may even result in constant time execution.

mysql-test/r/range.result

@@ -556,11 +556,42 @@ count(*)
 0
 select count(*) from t1 where x > -16;
 count(*)
-1
+2
 select count(*) from t1 where x = 18446744073709551601;
 count(*)
 1
 drop table t1;
+create table t1 (a bigint unsigned);
+create index t1i on t1(a);
+insert into t1 select 18446744073709551615;
+insert into t1 select 18446744073709551614;
+explain select * from t1 where a <> -1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	t1i	t1i	9	NULL	2	Using where; Using index
+select * from t1 where a <> -1;
+a
+18446744073709551614
+18446744073709551615
+explain select * from t1 where a > -1 or a < -1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	t1i	t1i	9	NULL	2	Using where; Using index
+select * from t1 where a > -1 or a < -1;
+a
+18446744073709551614
+18446744073709551615
+explain select * from t1 where a > -1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	t1i	t1i	9	NULL	2	Using where; Using index
+select * from t1 where a > -1;
+a
+18446744073709551614
+18446744073709551615
+explain select * from t1 where a < -1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select * from t1 where a < -1;
+a
+drop table t1;
 set names latin1;
 create table t1 (a char(10), b text, key (a)) character set latin1;
 INSERT INTO t1 (a) VALUES

mysql-test/t/range.test

@@ -423,14 +423,30 @@ select count(*) from t1 where x=0;
 select count(*) from t1 where x<0;
 select count(*) from t1 where x < -16;
 select count(*) from t1 where x = -16;
-# The following query returns wrong value because the range optimizer can't
-# handle search on a signed value for an unsigned parameter. This will be fixed in
-# 5.0
 select count(*) from t1 where x > -16;
 select count(*) from t1 where x = 18446744073709551601;
 
 drop table t1;
 
+#
+# Bug #11185 incorrect comparison of unsigned int to signed constant
+#
+create table t1 (a bigint unsigned);
+create index t1i on t1(a);
+insert into t1 select 18446744073709551615;
+insert into t1 select 18446744073709551614;
+
+explain select * from t1 where a <> -1;
+select * from t1 where a <> -1;
+explain select * from t1 where a > -1 or a < -1;
+select * from t1 where a > -1 or a < -1;
+explain select * from t1 where a > -1;
+select * from t1 where a > -1;
+explain select * from t1 where a < -1;
+select * from t1 where a < -1;
+
+drop table t1;
+
 #
 # Bug #6045: Binary Comparison regression in MySQL 4.1
 # Binary searches didn't use a case insensitive index.

sql/opt_range.cc

@@ -960,7 +960,9 @@ get_mm_parts(PARAM *param, COND *cond_func, Field *field,
 	if (sel_arg->type == SEL_ARG::IMPOSSIBLE)
 	{
 	  tree->type=SEL_TREE::IMPOSSIBLE;
-	  DBUG_RETURN(tree);
+          /* If this is an NE_FUNC, we still need to check GT_FUNC. */
+          if (!ne_func)
+            DBUG_RETURN(tree);
 	}
       }
       else
@@ -979,8 +981,9 @@ get_mm_parts(PARAM *param, COND *cond_func, Field *field,
     SEL_TREE *tree2= get_mm_parts(param, cond_func,
 				  field, Item_func::GT_FUNC,
                                   value, cmp_type);
-    if (tree2)
-      tree= tree_or(param,tree,tree2);
+    if (!tree2)
+      DBUG_RETURN(0)
+    tree= tree_or(param,tree,tree2);
   }
   DBUG_RETURN(tree);
 }
@@ -1159,6 +1162,35 @@ get_mm_leaf(PARAM *param, COND *conf_func, Field *field, KEY_PART *key_part,
   if (!(tree=new SEL_ARG(field,str,str2)))
     DBUG_RETURN(0);		// out of memory
 
+  /*
+    Check if we are comparing an UNSIGNED integer with a negative constant.
+    In this case we know that:
+    (a) (unsigned_int [< | <=] negative_constant) == FALSE
+    (b) (unsigned_int [> | >=] negative_constant) == TRUE
+    In case (a) the condition is false for all values, and in case (b) it
+    is true for all values, so we can avoid unnecessary retrieval and condition
+    testing, and we also get correct comparison of unsinged integers with
+    negative integers (which otherwise fails because at query execution time
+    negative integers are cast to unsigned if compared with unsigned).
+   */
+  Item_result field_result_type= field->result_type();
+  Item_result value_result_type= value->result_type();
+  if (field_result_type == INT_RESULT && value_result_type == INT_RESULT &&
+      ((Field_num*)field)->unsigned_flag && !((Item_int*)value)->unsigned_flag)
+  {
+    longlong item_val= value->val_int();
+    if (item_val < 0)
+    {
+      if (type == Item_func::LT_FUNC || type == Item_func::LE_FUNC)
+      {
+        tree->type= SEL_ARG::IMPOSSIBLE;
+        DBUG_RETURN(tree);
+      }
+      if (type == Item_func::GT_FUNC || type == Item_func::GE_FUNC)
+        DBUG_RETURN(0);
+    }
+  }
+
   switch (type) {
   case Item_func::LT_FUNC:
     if (field_is_equal_to_item(field,value))