Fix for BUG#7425.

The reported problems were due to two completely unrelated omissions.
1) The file sort procedure didn't correctly create the sort key in
   make_sortkey when the sortkey was an unsigned integer.
2) The name resolution procedure for column references inside a HAVING
   clause did not propagate the unsigned_flag of the resolved references.
This patch corrects both problems.

mysql-test/r/select.result

@@ -2422,3 +2422,26 @@ SELECT * FROM t1 WHERE city LIKE '%london%' AND city='London';
 city
 London
 DROP TABLE t1;
+create table t1 (a int(11) unsigned, b int(11) unsigned);
+insert into t1 values (1,0), (1,1), (1,2);
+select a-b  from t1 order by 1;
+a-b
+0
+1
+18446744073709551615
+select a-b , (a-b < 0)  from t1 order by 1;
+a-b	(a-b < 0)
+0	0
+1	0
+18446744073709551615	0
+select a-b as d, (a-b >= 0), b from t1 group by b having d >= 0;
+d	(a-b >= 0)	b
+1	1	0
+0	1	1
+18446744073709551615	1	2
+select cast((a - b) as unsigned) from t1 order by 1;
+cast((a - b) as unsigned)
+0
+1
+18446744073709551615
+drop table t1;

mysql-test/t/select.test

@@ -1964,3 +1964,14 @@ SELECT * FROM t1 WHERE city LIKE '%london%' AND city='London';
 
 DROP TABLE t1;
 
+#
+# Bug#7425 inconsistent sort order on unsigned columns result of substraction
+#
+
+create table t1 (a int(11) unsigned, b int(11) unsigned);
+insert into t1 values (1,0), (1,1), (1,2);
+select a-b  from t1 order by 1;
+select a-b , (a-b < 0)  from t1 order by 1;
+select a-b as d, (a-b >= 0), b from t1 group by b having d >= 0;
+select cast((a - b) as unsigned) from t1 order by 1;
+drop table t1;

sql/filesort.cc

@@ -656,12 +656,18 @@ static void make_sortkey(register SORTPARAM *param,
 	  to[3]= (uchar) (value >> 32);
 	  to[2]= (uchar) (value >> 40);
 	  to[1]= (uchar) (value >> 48);
-	  to[0]= (uchar) (value >> 56) ^ 128;	// Fix sign
+          if (item->unsigned_flag)                    /* Fix sign */
+            to[0]= (uchar) (value >> 56);
+          else
+            to[0]= (uchar) (value >> 56) ^ 128;	/* Reverse signbit */
 #else
 	  to[3]= (uchar) value;
 	  to[2]= (uchar) (value >> 8);
 	  to[1]= (uchar) (value >> 16);
-	  to[0]= (uchar) (value >> 24) ^ 128;	// Fix sign
+          if (item->unsigned_flag)                    /* Fix sign */
+            to[0]= (uchar) (value >> 24);
+          else
+            to[0]= (uchar) (value >> 24) ^ 128;	/* Reverse signbit */
 #endif
 	  break;
 	}

sql/item.cc

@@ -2281,6 +2281,7 @@ void Item_ref::set_properties()
   decimals=   (*ref)->decimals;
   collation.set((*ref)->collation);
   with_sum_func= (*ref)->with_sum_func;
+  unsigned_flag= (*ref)->unsigned_flag;
   fixed= 1;
 }