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)
