lesson03数据库
1 #视频1-数据库 2 1，跟视频添加表student数据 ---mysql(三)高级查询.md 3 2，修改mysql登陆密码、 ----mysql重置密码.md 4 3，typora下载 5 4，web图片墙 6 127.0.0.1:8888/index //网页游览 前端页面美食图片 7 root 8 123456 9 10 mysql> show tables; 11 +-----------------+ 12 | Tables_in_juhao | 13 +-----------------+ 14 | student | 15 | student02 | 16 +-----------------+ 17 2 rows in set (0.00 sec) 18 19 mysql> select *from student; 20 +-----------+-----------+-------+-----+-----------+ 21 | number | name | klass | age | gradName | 22 +-----------+-----------+-------+-----+-----------+ 23 | 201804001 | 刘一 | 19 | 16 | 二年级 | 24 | 201804002 | 陈二 | 18 | 19 | 一年级 | 25 | 201804003 | 张三 | 19 | 20 | 二年级 | 26 | 201804004 | 李四 | 19 | 17 | 一年级 | 27 | 201804005 | 王五 | 19 | 18 | 三年级 | 28 | 201804006 | 赵六 | 18 | 24 | 二年级 | 29 | 201804007 | 孙七 | 19 | 22 | 三年级 | 30 | 201804008 | 周八 | 19 | 21 | 二年级 | 31 | 201804009 | 吴九 | 18 | 25 | 一年级 | 32 | 201804010 | 郑十 | 19 | 23 | 一年级 | 33 | 201804011 | 小周周 | 18 | 20 | 二年级 | 34 | 201804012 | 周周周 | 19 | 21 | 三年级 | 35 +-----------+-----------+-------+-----+-----------+ 36 12 rows in set (0.00 sec) 37 38 39 40 -------------------------------------------------- 41 #视频2-筛选条件 42 where is null 43 where is not null 44 and，or ，not 45 where age between 18 and 20；//范围的值 46 where age in (18,20); //里面的值 47 where name like '周%' //模糊查询 正则匹配 % -任意多个字符 48 where name like '周_' //模糊查询 正则匹配 _ -任意一个字符 49 select * from student order by age[asc/desc] //排序 50 select distinct age from student; //去重查看 51 52 53 #视频3-聚合与分组 54 聚合函数 55 select count(age) from student; 统计个数 56 sum(age) 57 max(age) 58 min(age) 59 avg(age) 60 group_concat(age) //列出字段全部值 61 62 分组函数 63 select age from student group by age; 64 select age,max(number) from student group by age; 65 select age,max(number) from student group by age having count(number)=4; //having 限制输出结果，可以别名 66 select age,max(number) as new_number from student group by age having count(number)=4; //别名 67 select age as new_age from student where age>3 group by age; 68 执行顺序：where--聚合函数--having
1 ------------------------------------------------------------- 2 #视频5--pycharm程序操作数据库 3 限制与分页 4 select * from student limit 5; //显示5条数据 5 select * from student limit 5，6; //从第5条后，显示6条数据 6 7 n=1 #第几页 8 m=5 #5条数据 9 select * from student limit (n-1)*m，m; // 相当于 limit 0，5； 10 11 7分钟：--安装pymysql 12 workon py3env //必须进入环境装 13 pip install --upgrade pip //升级pip 14 pip install pymysql 15 pip list //查看装的库 16 deactivate //退出虚拟环境 17 mysql -uroot -pqwe123 18 19 pymysql连接数据库： //本地/远程 20 看-----程序操作数据库.md文件
------------------------------------------------
#03连接mysql.py --写程序：
1 import pymysql 2 3 db_config = { 4 'host':'127.0.0.1', 5 'user':'root', 6 'password':'qwe123', 7 'db':'juhao', # 8 'charset':'utf8' 9 } 10 11 conn = pymysql.connect(**db_config) #连接 12 cursor = conn.cursor() #生成一个游标 13 14 sql = "select * from student" 15 result = cursor.execute(sql) #通过这个方法来执行SQL语句 16 17 data = cursor.fetchall() #拿到我们执行sql语句获得的结果 18 19 for i in data: 20 print(i) 21 22 cursor.close() 23 conn.close()
#运行：
(201804001, '刘一', 19, 16, '二年级')
(201804002, '陈二', 18, 19, '一年级')
(201804003, '张三', 19, 20, '二年级')
(201804004, '李四', 19, 17, '一年级')
(201804005, '王五', 19, 18, '三年级')
(201804006, '赵六', 18, 24, '二年级')
(201804007, '孙七', 19, 22, '三年级')
(201804008, '周八', 19, 21, '二年级')
(201804009, '吴九', 18, 25, '一年级')
(201804010, '郑十', 19, 23, '一年级')
(201804011, '小周周', 18, 20, '二年级')
(201804012, '周周周', 19, 21, '三年级')
-----------------------------------------
1 #作业： 2 从课堂上演示的student表里面 3 4 1. 统计出每个年级分别有多少人 5 2.统计出每个年级age大于18的人数 6 3. 统计出一年级的人数 7 4. 统计出一年级age大于18的人数 8 9 MAX 用程序完成上面的操作 10 11 mysql> select gradName from student group by gradName; 12 +-----------+ 13 | gradName | 14 +-----------+ 15 | 一年级 | 16 | 三年级 | 17 | 二年级 | 18 +-----------+ 19 3 rows in set (0.00 sec) 20 21 mysql> select count(gradName),gradName from student group by gradName; 22 +-----------------+-----------+ 23 | count(gradName) | gradName | 24 +-----------------+-----------+ 25 | 4 | 一年级 | 26 | 3 | 三年级 | 27 | 5 | 二年级 | 28 +-----------------+-----------+ 29 3 rows in set (0.00 sec) 30 31 mysql> select count(age) from student where age>18; 32 +------------+ 33 | count(age) | 34 +------------+ 35 | 9 | 36 +------------+ 37 1 row in set (0.00 sec) 38 39 mysql> select count(gradName) from student where gradName="一年级"; 40 +-----------------+ 41 | count(gradName) | 42 +-----------------+ 43 | 4 | 44 +-----------------+ 45 1 row in set (0.00 sec) 46 47 mysql> select count(gradName) from student where gradName="一年级" and age>18; 48 +-----------------+ 49 | count(gradName) | 50 +-----------------+ 51 | 3 | 52 +-----------------+ 53 1 row in set (0.00 sec)