sql_select.cc:

  Fixed bug #12885.
  Forced inheritence of the maybe_null flag for the expressions
  containing GROUP BY attributes in selects with ROLLUP.
olap.test, olap.result:
  Added test case for bug #12885.

mysql-test/r/olap.result

@@ -516,3 +516,16 @@ a	b	c	count
 1	NULL	NULL	2
 NULL	NULL	NULL	2
 DROP TABLE t1;
+CREATE TABLE t1 (a int(11) NOT NULL);
+INSERT INTO t1 VALUES (1),(2);
+SELECT * FROM (SELECT a, a + 1, COUNT(*) FROM t1 GROUP BY a WITH ROLLUP) t;
+a	a + 1	COUNT(*)
+1	2	1
+2	3	1
+NULL	NULL	2
+SELECT * FROM (SELECT a, LENGTH(a), COUNT(*) FROM t1 GROUP BY a WITH ROLLUP) t;
+a	LENGTH(a)	COUNT(*)
+1	1	1
+2	1	1
+NULL	NULL	2
+DROP TABLE t1;

mysql-test/t/olap.test

@@ -250,4 +250,17 @@ SELECT a, b, a AS c, COUNT(*) AS count FROM t1 GROUP BY a, b, c WITH ROLLUP;
 
 DROP TABLE t1;
 
+#
+# Bug #11885:  derived table specified by a subquery with
+#              ROLLUP over expressions on not nullable group by attributes 
+#
+
+CREATE TABLE t1 (a int(11) NOT NULL);
+INSERT INTO t1 VALUES (1),(2);
+
+SELECT * FROM (SELECT a, a + 1, COUNT(*) FROM t1 GROUP BY a WITH ROLLUP) t;
+SELECT * FROM (SELECT a, LENGTH(a), COUNT(*) FROM t1 GROUP BY a WITH ROLLUP) t;
+
+DROP TABLE t1;
+
 # End of 4.1 tests

sql/sql_select.cc

@@ -9277,6 +9277,8 @@ void free_underlaid_joins(THD *thd, SELECT_LEX *select)
     The function replaces occurrences of group by fields in expr
     by ref objects for these fields unless they are under aggregate
     functions.
+    The function also corrects value of the the maybe_null attribute
+    for the items of all subexpressions containing group by fields.
 
   IMPLEMENTATION
     The function recursively traverses the tree of the expr expression,
@@ -9287,6 +9289,9 @@ void free_underlaid_joins(THD *thd, SELECT_LEX *select)
     This substitution is needed GROUP BY queries with ROLLUP if
     SELECT list contains expressions over group by attributes.
 
+  TODO: Some functions are not null-preserving. For those functions
+    updating of the maybe_null attribute is an overkill. 
+
   EXAMPLES
     SELECT a+1 FROM t1 GROUP BY a WITH ROLLUP
     SELECT SUM(a)+a FROM t1 GROUP BY a WITH ROLLUP 
@@ -9307,6 +9312,7 @@ static bool change_group_ref(THD *thd, Item_func *expr, ORDER *group_list,
          arg != arg_end; arg++)
     {
       Item *item= *arg;
+      bool arg_changed= FALSE;
       if (item->type() == Item::FIELD_ITEM || item->type() == Item::REF_ITEM)
       {
         ORDER *group_tmp;
@@ -9318,15 +9324,20 @@ static bool change_group_ref(THD *thd, Item_func *expr, ORDER *group_list,
             if(!(new_item= new Item_ref(group_tmp->item, 0, item->name)))
               return 1;                                 // fatal_error is set
             thd->change_item_tree(arg, new_item);
-            *changed= TRUE;
+            arg_changed= TRUE;
           }
         }
       }
       else if (item->type() == Item::FUNC_ITEM)
       {
-        if (change_group_ref(thd, (Item_func *) item, group_list, changed))
+        if (change_group_ref(thd, (Item_func *) item, group_list, &arg_changed))
           return 1;
       }
+      if (arg_changed)
+      {
+        expr->maybe_null= 1;
+        *changed= TRUE;
+      }
     }
   }
   return 0;
@@ -9389,7 +9400,7 @@ bool JOIN::rollup_init()
     }
     if (item->type() == Item::FUNC_ITEM)
     {
-      bool changed= 0;
+      bool changed= FALSE;
       if (change_group_ref(thd, (Item_func *) item, group_list, &changed))
         return 1;
       /*