mysql> select * from table1;+----------+------------+-----+---------------------+| name_new | transactor | pid | order_date          |+----------+------------+-----+---------------------+| 1hahha   | 1xiaohong  |   1 | 2019-08-04 20:45:47 || 2hahha   | 2xiaohong  |   2 | 2019-08-04 20:45:57 || 3hahha   | 3xiaohong  |   3 | 2019-08-04 20:46:02 || 4hahha   | 4xiaohong  |   4 | 2019-08-04 20:46:05 || 3hahha   | bob        |   5 | 2019-08-04 20:46:08 || 3hahha   | lee        |   6 | 2019-08-04 20:46:12 |+----------+------------+-----+---------------------+6 rows in set (0.00 sec)mysql> select avg(pid) from table1;+----------+| avg(pid) |+----------+|   3.5000 |+----------+1 row in set (0.00 sec)mysql> select (21/6);+--------+| (21/6) |+--------+| 3.5000 |+--------+1 row in set (0.00 sec)