Merge epotemkin@bk-internal.mysql.com:/home/bk/mysql-4.1

into moonbone.local:/work/12861-bug-4.1-mysql

mysql-test/r/func_gconcat.result

@@ -548,3 +548,6 @@ FROM t1 JOIN t2 ON t1.bID = t2.bID;
 COUNT(*)	GROUP_CONCAT(DISTINCT t2.somename SEPARATOR ' |')
 2	test
 DROP TABLE t1,t2;
+select * from (select group_concat('c') from DUAL) t;
+group_concat('c')
+NULL

mysql-test/t/func_gconcat.test

@@ -343,4 +343,9 @@ SELECT COUNT(*), GROUP_CONCAT(DISTINCT t2.somename SEPARATOR ' |')
 
 DROP TABLE t1,t2;
 
+#
+# Bug #12861 hang with group_concat insubquery FROM DUAL
+#
+select * from (select group_concat('c') from DUAL) t;
+
 # End of 4.1 tests

sql/item_sum.cc

@@ -1916,7 +1916,7 @@ Item_func_group_concat::fix_fields(THD *thd, TABLE_LIST *tables, Item **ref)
   }
   
   thd->allow_sum_func= 0;
-  maybe_null= 0;
+  maybe_null= 1;
   item_thd= thd;
 
   /*
@@ -1929,8 +1929,6 @@ Item_func_group_concat::fix_fields(THD *thd, TABLE_LIST *tables, Item **ref)
          args[i]->fix_fields(thd, tables, args + i)) ||
         args[i]->check_cols(1))
       return 1;
-    if (i < arg_count_field)
-      maybe_null|= args[i]->maybe_null;
   }
 
   if (agg_item_charsets(collation, func_name(),