Bug#50591 bit(31) causes Duplicate entry '1-NULL' for key 'group_key'

The problem is that during temporary table creation uneven bits
are not taken into account for hidden fields. It leads to incorrect
calculation&allocation of null bytes size for table record. And
if grouped value is null we set wrong bit for this value(see end_update()).
Fixed by adding separate calculation of uneven bit for hidden fields.

mysql-test/r/type_bit.result

@@ -785,4 +785,19 @@ t1	CREATE TABLE `t1` (
   KEY `a` (`a`)
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
+#
+# Bug#50591 bit(31) causes Duplicate entry '1-NULL' for key 'group_key'
+#
+CREATE TABLE t1(a INT, b BIT(7) NOT NULL);
+INSERT INTO t1 VALUES (NULL, 0),(NULL, 0);
+SELECT SUM(a) FROM t1 GROUP BY b, a;
+SUM(a)
+NULL
+DROP TABLE t1;
+CREATE TABLE t1(a INT, b BIT(7) NOT NULL, c BIT(8) NOT NULL);
+INSERT INTO t1 VALUES (NULL, 0, 0),(NULL, 0, 0);
+SELECT SUM(a) FROM t1 GROUP BY c, b, a;
+SUM(a)
+NULL
+DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/type_bit.test

@@ -425,4 +425,17 @@ select hex(a) from t1;
 show create table t1;
 drop table t1;
 
+--echo #
+--echo # Bug#50591 bit(31) causes Duplicate entry '1-NULL' for key 'group_key'
+--echo #
+CREATE TABLE t1(a INT, b BIT(7) NOT NULL);
+INSERT INTO t1 VALUES (NULL, 0),(NULL, 0);
+SELECT SUM(a) FROM t1 GROUP BY b, a;
+DROP TABLE t1;
+
+CREATE TABLE t1(a INT, b BIT(7) NOT NULL, c BIT(8) NOT NULL);
+INSERT INTO t1 VALUES (NULL, 0, 0),(NULL, 0, 0);
+SELECT SUM(a) FROM t1 GROUP BY c, b, a;
+DROP TABLE t1;
+
 --echo End of 5.1 tests

sql/sql_select.cc

@@ -9822,7 +9822,11 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
   KEY_PART_INFO *key_part_info;
   Item **copy_func;
   MI_COLUMNDEF *recinfo;
-  uint total_uneven_bit_length= 0;
+  /*
+    total_uneven_bit_length is uneven bit length for visible fields
+    hidden_uneven_bit_length is uneven bit length for hidden fields
+  */
+  uint total_uneven_bit_length= 0, hidden_uneven_bit_length= 0;
   bool force_copy_fields= param->force_copy_fields;
   /* Treat sum functions as normal ones when loose index scan is used. */
   save_sum_fields|= param->precomputed_group_by;
@@ -10099,6 +10103,14 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
       */
       param->hidden_field_count= fieldnr;
       null_count= 0;
+      /*
+        On last hidden field we store uneven bit length in
+        hidden_uneven_bit_length and proceed calculation of
+        uneven bits for visible fields into
+        total_uneven_bit_length variable.
+      */
+      hidden_uneven_bit_length= total_uneven_bit_length;
+      total_uneven_bit_length= 0;
     }
   }
   DBUG_ASSERT(fieldnr == (uint) (reg_field - table->field));
@@ -10144,7 +10156,8 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
     else
       null_count++;
   }
-  hidden_null_pack_length=(hidden_null_count+7)/8;
+  hidden_null_pack_length= (hidden_null_count + 7 +
+                            hidden_uneven_bit_length) / 8;
   null_pack_length= (hidden_null_pack_length +
                      (null_count + total_uneven_bit_length + 7) / 8);
   reclength+=null_pack_length;