1.一些多表查询的练习题
2.pymysql模块
3.sql注入问题
4.增删改查
一.一些多表查询的练习题
首先用Navicat导入数据：
1 /* 2 数据导入： 3 Navicat Premium Data Transfer 4 5 Source Server : localhost 6 Source Server Type : MySQL 7 Source Server Version : 50624 8 Source Host : localhost 9 Source Database : sqlexam 10 11 Target Server Type : MySQL 12 Target Server Version : 50624 13 File Encoding : utf-8 14 15 Date: 10/21/2016 06:46:46 AM 16 */ 17 18 SET NAMES utf8; 19 SET FOREIGN_KEY_CHECKS = 0; 20 21 -- ---------------------------- 22 -- Table structure for `class` 23 -- ---------------------------- 24 DROP TABLE IF EXISTS `class`; 25 CREATE TABLE `class` ( 26 `cid` int(11) NOT NULL AUTO_INCREMENT, 27 `caption` varchar(32) NOT NULL, 28 PRIMARY KEY (`cid`) 29 ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8; 30 31 -- ---------------------------- 32 -- Records of `class` 33 -- ---------------------------- 34 BEGIN; 35 INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班'); 36 COMMIT; 37 38 -- ---------------------------- 39 -- Table structure for `course` 40 -- ---------------------------- 41 DROP TABLE IF EXISTS `course`; 42 CREATE TABLE `course` ( 43 `cid` int(11) NOT NULL AUTO_INCREMENT, 44 `cname` varchar(32) NOT NULL, 45 `teacher_id` int(11) NOT NULL, 46 PRIMARY KEY (`cid`), 47 KEY `fk_course_teacher` (`teacher_id`), 48 CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`) 49 ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8; 50 51 -- ---------------------------- 52 -- Records of `course` 53 -- ---------------------------- 54 BEGIN; 55 INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2'); 56 COMMIT; 57 58 -- ---------------------------- 59 -- Table structure for `score` 60 -- ---------------------------- 61 DROP TABLE IF EXISTS `score`; 62 CREATE TABLE `score` ( 63 `sid` int(11) NOT NULL AUTO_INCREMENT, 64 `student_id` int(11) NOT NULL, 65 `course_id` int(11) NOT NULL, 66 `num` int(11) NOT NULL, 67 PRIMARY KEY (`sid`), 68 KEY `fk_score_student` (`student_id`), 69 KEY `fk_score_course` (`course_id`), 70 CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`), 71 CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`) 72 ) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8; 73 74 -- ---------------------------- 75 -- Records of `score` 76 -- ---------------------------- 77 BEGIN; 78 INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87'); 79 COMMIT; 80 81 -- ---------------------------- 82 -- Table structure for `student` 83 -- ---------------------------- 84 DROP TABLE IF EXISTS `student`; 85 CREATE TABLE `student` ( 86 `sid` int(11) NOT NULL AUTO_INCREMENT, 87 `gender` char(1) NOT NULL, 88 `class_id` int(11) NOT NULL, 89 `sname` varchar(32) NOT NULL, 90 PRIMARY KEY (`sid`), 91 KEY `fk_class` (`class_id`), 92 CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`) 93 ) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8; 94 95 -- ---------------------------- 96 -- Records of `student` 97 -- ---------------------------- 98 BEGIN; 99 INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四'); 100 COMMIT; 101 102 -- ---------------------------- 103 -- Table structure for `teacher` 104 -- ---------------------------- 105 DROP TABLE IF EXISTS `teacher`; 106 CREATE TABLE `teacher` ( 107 `tid` int(11) NOT NULL AUTO_INCREMENT, 108 `tname` varchar(32) NOT NULL, 109 PRIMARY KEY (`tid`) 110 ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8; 111 112 -- ---------------------------- 113 -- Records of `teacher` 114 -- ---------------------------- 115 BEGIN; 116 INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师'); 117 COMMIT; 118 119 SET FOREIGN_KEY_CHECKS = 1;
拷贝上述代码，新建一个.sql文件，保存到桌面
打开navicat新建数据库day41，选中新建的数据库鼠标右键选择运行SQL文件
弹出文件框，选中刚刚保存到桌面的.sql文件即可
练习题：
1 1、查询所有的课程的名称以及对应的任课老师姓名 2 4、查询平均成绩大于八十分的同学的姓名和平均成绩 3 7、 查询没有报李平老师课的学生姓名 4 8、 查询没有同时选修物理课程和体育课程的学生姓名 5 9、 查询挂科超过两门(包括两门)的学生姓名和班级 6 # 参考答案 7 #1、查询所有的课程的名称以及对应的任课老师姓名 8 SELECT 9 course.cname, 10 teacher.tname 11 FROM 12 course 13 INNER JOIN teacher ON course.teacher_id = teacher.tid; 14 #4、查询平均成绩大于八十分的同学的姓名和平均成绩 15 SELECT 16 student.sname, 17 t1.avg_num 18 FROM 19 student 20 INNER JOIN ( 21 SELECT 22 student_id, 23 avg(num) AS avg_num 24 FROM 25 score 26 GROUP BY 27 student_id 28 HAVING 29 avg(num) > 80 30 ) AS t1 ON student.sid = t1.student_id; 31 #7、 查询没有报李平老师课的学生姓名(找出报名李平老师课程的学生，然后取反就可以) 32 SELECT 33 student.sname 34 FROM 35 student 36 WHERE 37 sid NOT IN ( 38 SELECT DISTINCT 39 student_id 40 FROM 41 score 42 WHERE 43 course_id IN ( 44 SELECT 45 course.cid 46 FROM 47 course 48 INNER JOIN teacher ON course.teacher_id = teacher.tid 49 WHERE 50 teacher.tname = '李平老师' 51 ) 52 ); 53 #8、 查询没有同时选修物理课程和体育课程的学生姓名(没有同时选修指的是选修了一门的，思路是得到物理+体育课程的学生信息表，然后基于学生分组，统计count(课程)=1) 54 SELECT 55 student.sname 56 FROM 57 student 58 WHERE 59 sid IN ( 60 SELECT 61 student_id 62 FROM 63 score 64 WHERE 65 course_id IN ( 66 SELECT 67 cid 68 FROM 69 course 70 WHERE 71 cname = '物理' 72 OR cname = '体育' 73 ) 74 GROUP BY 75 student_id 76 HAVING 77 COUNT(course_id) = 1 78 ); 79 80 # 9、 查询挂科超过两门(包括两门)的学生姓名和班级 81 select student.sname,class.caption from class INNER JOIN student 82 on class.cid = student.class_id 83 WHERE student.sid in 84 (select student_id from score where num < 60 85 GROUP BY student_id 86 HAVING COUNT(course_id) >=2) 87 ;
二.pymysql模块
# 模块:pymysql import pymysql conn = pymysql.connect( host = '127.0.0.1', port = 3306, user = 'root', password = '123', database = 'day38', charset = 'utf8' # 编码千万不要加- 如果写成了utf-8会直接报错 ) cursor = conn.cursor(pymysql.cursors.DictCursor) # 产生一个游标对象 以字典的形式返回查询出来的数据 键是表的字段 值是表的字段对应的信息 sql = 'select * from teacher' cursor.execute(sql) # 执行传入的sql语句 # print(res) # res是执行语句返回的数据条数 print(cursor.fetchone()) # 只获取一条数据 print(cursor.fetchone()) # 只获取一条数据 print(cursor.fetchone()) # 只获取一条数据 # cursor.scroll(2,'absolute') # 控制光标移动 absolute相对于其实位置 往后移动几位 cursor.scroll(1,'relative') # relative相对于当前位置 往后移动几位 print(cursor.fetchall()) # 获取所有的数据 返回的结果是一个列表
三.sql注入 即 增删改查
import pymysql conn = pymysql.connect( host = '127.0.0.1', port = 3306, user = 'root', password = '123', database = 'day38', charset = 'utf8', # 编码千万不要加- 如果写成了utf-8会直接报错 autocommit = True # 这个参数配置完成后 增删改操作都不需要在手动加conn.commit了 ) cursor = conn.cursor(pymysql.cursors.DictCursor) # 产生一个游标对象 以字典的形式返回查询出来的数据 键是表的字段 值是表的字段对应的信息 # sql = 'insert into user(name,password) values("jerry","666")' # sql = 'update user set name = "jasonhs" where id = 1' sql = 'delete from user where id = 6' cursor.execute(sql) """ 增删改操作 都必须加一句 conn.commit()操作 """ # conn.commit() # username = input('username>>>:') # password = input('password>>>:') # sql = "select * from user where name =%s and password = %s" # print(sql) # res = cursor.execute(sql,(username,password)) # 能够帮你自动过滤特殊符号 避免sql注入的问题 # # execute 能够自动识别sql语句中的%s 帮你做替换 # if res: # print(cursor.fetchall()) # else: # print('用户名或密码错误') """ sql注入 就是利用注释等具有特殊意义的符号 来完成一些骚操作 后续写sql语句 不要手动拼接关键性的数据 而是让excute帮你去做拼接 """