MySQL中的WITH ROLLUP
MySQL的扩展SQL中有一个非常有意思的应用WITH ROLLUP，在分组的统计数据的基础上再进行相同的统计（SUM,AVG,COUNT…），非常类似于Oracle中统计函数的功能，Oracle的统计函数更多更强大。
下面演示单个司机以及所有司机的总行驶里程数和平均行驶里程数：
mysql> select name,sum(miles) as 'miles/driver'
-> from driver_log group by name with rollup;
+-------+--------------+
| name | miles/driver |
+-------+--------------+
| Ben | 362 |
| Henry | 911 |
| Suzi | 893 |
| NULL | 2166 |
+-------+--------------+
4 rows in set (0.00 sec)
mysql> select name,avg(miles) as driver_avg
-> from driver_log group by name with rollup;
+-------+------------+
| name | driver_avg |
+-------+------------+
| Ben | 120.6667 |
| Henry | 182.2000 |
| Suzi | 446.5000 |
| NULL | 216.6000 |
+-------+------------+
4 rows in set (0.00 sec)
mysql> select name,sum(miles) as 'miles/driver',avg(miles) as driver_avg
-> from driver_log group by name with rollup;
+-------+--------------+------------+
| name | miles/driver | driver_avg |
+-------+--------------+------------+
| Ben | 362 | 120.6667 |
| Henry | 911 | 182.2000 |
| Suzi | 893 | 446.5000 |
| NULL | 2166 | 216.6000 |
+-------+--------------+------------+
4 rows in set (0.00 sec)
在多个分组下WITH ROLLUP同样有效：
mysql> select srcuser,dstuser,count(*) from mail group by srcuser,dstuser;
+---------+---------+----------+
| srcuser | dstuser | count(*) |
+---------+---------+----------+
| barb | barb | 1 |
| barb | tricia | 2 |
| gene | barb | 2 |
| gene | gene | 3 |
| gene | tricia | 1 |
| phil | barb | 1 |
| phil | phil | 2 |
| phil | tricia | 2 |
| tricia | gene | 1 |
| tricia | phil | 1 |
+---------+---------+----------+
10 rows in set (0.05 sec)
mysql> select srcuser,dstuser,count(*) from mail group by srcuser,dstuser with rollup;
+---------+---------+----------+
| srcuser | dstuser | count(*) |
+---------+---------+----------+
| barb | barb | 1 |
| barb | tricia | 2 |
| barb | NULL | 3 |
| gene | barb | 2 |
| gene | gene | 3 |
| gene | tricia | 1 |
| gene | NULL | 6 |
| phil | barb | 1 |
| phil | phil | 2 |
| phil | tricia | 2 |
| phil | NULL | 5 |
| tricia | gene | 1 |
| tricia | phil | 1 |
| tricia | NULL | 2 |
| NULL | NULL | 16 |
+---------+---------+----------+
15 rows in set (0.00 sec)