mysql使用

Posted 2021-10-08 小卓卓的世界

1、 导入hellodb.sql生成数据库
(1) 在students表中，查询年龄大于25岁，且为男性的同学的名字和年龄

mysql> select * from students;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name          | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL |
+-------+---------------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

mysql> select name,age from students where age > 25 and Gender=\'m\';
+--------------+-----+
| name         | age |
+--------------+-----+
| Xie Yanke    |  53 |
| Ding Dian    |  32 |
| Yu Yutong    |  26 |
| Shi Qing     |  46 |
| Tian Boguang |  33 |
| Xu Xian      |  27 |
| Sun Dasheng  | 100 |
+--------------+-----+
7 rows in set (0.00 sec)

(2) 以ClassID为分组依据，显示每组的平均年龄

mysql> SELECT classid,AVG(age) FROM students WHERE classid IS NOT NULL GROUP BY classid;
+---------+----------+
| classid | AVG(age) |
+---------+----------+
|       2 |  36.0000 |
|       1 |  20.5000 |
|       4 |  24.7500 |
|       3 |  20.2500 |
|       5 |  46.0000 |
|       7 |  19.6667 |
|       6 |  20.7500 |
+---------+----------+
7 rows in set (0.00 sec)

(3) 显示第2题中平均年龄大于30的分组及平均年龄

mysql> select classid,AVG(age) as avgage from students where classid is not null group by classid having avgage > 30;
+---------+---------+
| classid | avgage  |
+---------+---------+
|       2 | 36.0000 |
|       5 | 46.0000 |
+---------+---------+
2 rows in set (0.01 sec)

(4) 显示以L开头的名字的同学的信息

mysql> SELECT * FROM students WHERE NAME LIKE \'l%\';
+-------+-------------+-----+--------+---------+-----------+
| StuID | Name        | Age | Gender | ClassID | TeacherID |
+-------+-------------+-----+--------+---------+-----------+
|     8 | Lin Daiyu   |  17 | F      |       7 |      NULL |
|    14 | Lu Wushuang |  17 | F      |       3 |      NULL |
|    17 | Lin Chong   |  25 | M      |       4 |      NULL |
+-------+-------------+-----+--------+---------+-----------+
3 rows in set (0.00 sec)

2、数据库授权magedu用户，允许192.168.1.0/24网段可以连接mysql

mysql> create user \'magedu\'@\'192.168.1.%\' identified by \'123456\';
Query OK, 0 rows affected (0.00 sec)
mysql> grant all privileges on `hellodb`.* to \'magedu\'@\'192.168.1.%\' identified by \'123456\';
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)