mysql group by with rollup，mysqlrollup

mysql group by with rollup，mysqlrollup

1、普通的 GROUP BY 操作，可以按照部門和職位進行分組，計算每個部門，每個職位的工資平均值：mysql> select dep,pos,avg(sal) from employee group by dep,pos;+------+------+-----------+| dep | pos | avg(sal) |+------+------+-----------+| 01 | 01 | 1500.0000 || 01 | 02 | 1950.0000 || 02 | 01 | 1500.0000 || 02 | 02 | 2450.0000 || 03 | 01 | 2500.0000 || 03 | 02 | 2550.0000 |+------+------+-----------+6 rows in set (0.02 sec)2、如果我們希望顯示部門的平均值和全部僱員的平均值，普通的 GROUP BY 語句是不能實現的，需要另外執行一個查詢操作，或者通過程式來計算。如果使用有 WITH ROLLUP 子句的 GROUP BY 語句，則可以輕鬆實現這個要求：mysql> select dep,pos,avg(sal) from employee group by dep,pos with rollup;+------+------+-----------+| dep | pos | avg(sal) |+------+------+-----------+| 01 | 01 | 1500.0000 || 01 | 02 | 1950.0000 || 01 | NULL | 1725.0000 || 02 | 01 | 1500.0000 || 02 | 02 | 2450.0000 || 02 | NULL | 2133.3333 || 03 | 01 | 2500.0000 || 03 | 02 | 2550.0000 || 03 | NULL | 2533.3333 || NULL | NULL | 2090.0000 |+------+------+-----------+10 rows in set (0.00 sec)