Fixed bug #9681.
  The bug happened with queries using derived tables specified by
  a SELECT with ROLLUP, such as:
  SELECT * FROM (SELECT a, SUM(a) FROM t1 GROUP BY a WITH ROLLUP) t2,
  if column a of table t1 is declared as NOT NULL.
  This was to the fact that the first column of the temporary table
  created to contain the derived table erroneously inherited the NOT NULL
  attribute from column a.
olap.result, olap.test:
  Added a test case for bug #9681.


mysql-test/t/olap.test:
  Added a test case for bug #9681.
mysql-test/r/olap.result:
  Added a test case for bug #9681.
sql/sql_select.cc:
  Fixed bug #9681.
  The bug happened with queries using derived tables specified by
  a SELECT with ROLLUP, such as:
  SELECT * FROM (SELECT a, SUM(a) FROM t1 GROUP BY a WITH ROLLUP) t2,
  if column a of table t1 is declared as NOT NULL.
  This was to the fact that the first column of the temporary table
  created to contain the derived table erroneously inherited the NOT NULL
  attribute from column a.