merge

mysql-test/r/metadata.result

 drop table if exists t1,t2;
 select 1, 1.0, -1, "hello", NULL;
 Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
-def					1	8	1	1	N	32769	0	8
-def					1.0	5	3	3	N	32769	1	8
-def					-1	8	2	2	N	32769	0	8
+def					1	8	1	1	N	32897	0	63
+def					1.0	5	3	3	N	32897	1	63
+def					-1	8	2	2	N	32897	0	63
 def					hello	253	5	5	N	1	31	8
 def					NULL	6	0	0	Y	32896	0	63
 1	1.0	-1	hello	NULL

sql/item_cmpfunc.cc

@@ -1119,6 +1119,9 @@ Item_func_nullif::fix_length_and_dec()
     max_length=args[0]->max_length;
     decimals=args[0]->decimals;
     agg_result_type(&cached_result_type, args, 2);
+    if (cached_result_type == STRING_RESULT &&
+        agg_arg_charsets(collation, args, arg_count, MY_COLL_CMP_CONV))
+      return;
   }
 }