MDEV-5719: Wrong result with GROUP BY and LEFT OUTER JOINmariadb-10.0.16

Merged revision 5224 from mysql-5.6 and added a test case.
..
revno: 5224
committer: Sergey Glukhov <sergey.glukhov@oracle.com>
branch nick: mysql-5.6
timestamp: Wed 2013-06-19 14:24:08 +0400
message:
    Bug#16620047 INCORRECT QUERY RESULT (AFTER SERVER UPGRADE)

1 files changed, 15 insertions, 8 deletions

diff --git a/sql/field.h b/sql/field.h
index dd603d41bf7..0390e95f954 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -656,21 +656,28 @@ public:
   inline bool is_null(my_ptrdiff_t row_offset= 0) const
   {
     /*
+      If the field is NULLable, it returns NULLity based
+      on null_ptr[row_offset] value. Otherwise it returns
+      NULL flag depending on TABLE::null_row value.
+
       The table may have been marked as containing only NULL values
       for all fields if it is a NULL-complemented row of an OUTER JOIN
       or if the query is an implicitly grouped query (has aggregate
       functions but no GROUP BY clause) with no qualifying rows. If
-      this is the case (in which TABLE::null_row is true), the field
-      is considered to be NULL.
+      this is the case (in which TABLE::null_row is true) and the
+      field is not nullable, the field is considered to be NULL.
+
+      Do not change the order of testing. Fields may be associated
+      with a TABLE object without being part of the current row.
+      For NULL value check to work for these fields, they must
+      have a valid null_ptr, and this pointer must be checked before
+      TABLE::null_row.
+
       Note that if a table->null_row is set then also all null_bits are
       set for the row.
-
-      Otherwise, if the field is NULLable, it has a valid null_ptr
-      pointer, and its NULLity is recorded in the "null_bit" bit of
-      null_ptr[row_offset].
     */
-    return (table->null_row ? TRUE :
-            null_ptr ? MY_TEST(null_ptr[row_offset] & null_bit) : 0);
+    return real_maybe_null() ?
+      MY_TEST(null_ptr[row_offset] & null_bit) : table->null_row;
   }
   inline bool is_real_null(my_ptrdiff_t row_offset= 0) const
     { return null_ptr ? (null_ptr[row_offset] & null_bit ? 1 : 0) : 0; }