mysql ，with rollup的用法

如下，可以看到使用后，也统计了null的个数。

mysql> select * from table1;
+----------+------------+-----+---------------------+
| name_new | transactor | pid | order_date          |
+----------+------------+-----+---------------------+
| 1hahha   | 1xiaohong  |    | -- :: |
| 2hahha   | 2xiaohong  |    | -- :: |
| 3hahha   | 3xiaohong  |    | -- :: |
| 4hahha   | 4xiaohong  |    | -- :: |
| 3hahha   | bob        |    | -- :: |
| 3hahha   | lee        |    | -- :: |
| 3hahha   | lee        |    | -- :: |
| 3hahha   | lee        |    | -- :: |
| 3hahha   | bob        |    | -- :: |
| 3hahha   | bob        |   | -- :: |
+----------+------------+-----+---------------------+
 rows in set (0.00 sec)

mysql> select transactor,count(*) as num from table1 group by transactor;
+------------+-----+
| transactor | num |
+------------+-----+
| 1xiaohong  |    |
| 2xiaohong  |    |
| 3xiaohong  |    |
| 4xiaohong  |    |
| bob        |    |
| lee        |    |
+------------+-----+
 rows in set (0.00 sec)

mysql> select transactor,count(*) as num from table1 group by transactor with rollup;
+------------+-----+
| transactor | num |
+------------+-----+
| 1xiaohong  |    |
| 2xiaohong  |    |
| 3xiaohong  |    |
| 4xiaohong  |    |
| bob        |    |
| lee        |    |
| NULL       |   |
+------------+-----+
 rows in set (0.01 sec)