func_str.result, func_str.test:

  Added a test case for bug #7751.
item_strfunc.cc:
  Fixed bug #7751.
  The function Item_func_conv::val_str did not update
  the unsigned_flag value.

mysql-test/r/func_str.result

@@ -703,3 +703,26 @@ NULL
 select trim('xyz' from null) as "must_be_null";
 must_be_null
 NULL
+CREATE TABLE t1 (
+id int(11) NOT NULL auto_increment,
+a bigint(20) unsigned default NULL,
+PRIMARY KEY  (id)
+) ENGINE=MyISAM;
+INSERT INTO t1 VALUES
+('0','16307858876001849059');
+SELECT CONV('e251273eb74a8ee3', 16, 10);
+CONV('e251273eb74a8ee3', 16, 10)
+16307858876001849059
+EXPLAIN 
+SELECT id
+FROM t1
+WHERE a = 16307858876001849059;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+EXPLAIN 
+SELECT id
+FROM t1
+WHERE a = CONV('e251273eb74a8ee3', 16, 10);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+DROP TABLE t1;

mysql-test/t/func_str.test

@@ -443,3 +443,30 @@ select quote(trim(concat('    ', 'a')));
 #
 select trim(null from 'kate') as "must_be_null";
 select trim('xyz' from null) as "must_be_null";
+
+#
+# Bug #7751 - conversion for a bigint unsigned constant 
+#
+
+CREATE TABLE t1 (
+  id int(11) NOT NULL auto_increment,
+  a bigint(20) unsigned default NULL,
+  PRIMARY KEY  (id)
+) ENGINE=MyISAM;
+
+INSERT INTO t1 VALUES
+('0','16307858876001849059');
+
+SELECT CONV('e251273eb74a8ee3', 16, 10);
+
+EXPLAIN 
+SELECT id
+  FROM t1
+  WHERE a = 16307858876001849059;
+
+EXPLAIN 
+  SELECT id
+  FROM t1
+  WHERE a = CONV('e251273eb74a8ee3', 16, 10);
+
+DROP TABLE t1;

sql/item_strfunc.cc

@@ -2171,6 +2171,7 @@ String *Item_func_conv::val_str(String *str)
     return 0;
   }
   null_value=0;
+  unsigned_flag= !(from_base < 0);
   if (from_base < 0)
     dec= my_strntoll(res->charset(),res->ptr(),res->length(),-from_base,&endptr,&err);
   else