• MySQL Navicat 使用


    昨日内容

    select distinct 字段1,字段2,。。。 from 表名
                where    分组之前的过滤条件
                group by 分组条件
                having    分组之后过滤条件
                order by 排序字段1 asc,排序字段2 desc
                limit 5,5
    
    as语法中给某个查询结果起别名的时候需要把查询语句中的分号去除
    (select name,salary*12 as '年薪' from emp) as t1;
    
    # 一个字段展示用户名和年龄
    select concat(name,':',age) as info from emp;
    
    # 字段为NAME和AGE,值为‘NAME:jason’,'AGE:18'
    select concat("NAME:",name) as NAME,concat("AGE:",age) as AGE from emp;
    
    # 如果拼接的符号是统一的可以用
    select concat_ws(':',name,age,sex) as info from emp;
    
    # 1.子查询相关
    # 查询平均年轻在25岁以上的部门名
    select name from dep 
                where id in 
                (select dep_id from emp group by dep_id having avg(age)>25);
    
    select dep.name from emp inner join dep on emp.dep_id = dep.id 
                group by dep.name
                having avg(age) > 25;
    
    # exist(了解)
    EXISTS关字键字表示存在。在使用EXISTS关键字时,内层查询语句不返回查询的记录,
    而是返回一个真假值,True或False。
    当返回True时,外层查询语句将进行查询
    当返回值为False时,外层查询语句不进行查询。
    select * from employee
        where exists
        (select id from department where id > 3);
    
    select * from employee
        where exists
        (select id from department where id > 250);
    View Code

    Navicat使用

    下载地址:https://pan.baidu.com/s/1bpo5mqj

    掌握:
    #1. 测试+链接数据库
    #2. 新建库
    #3. 新建表,新增字段+类型+约束
    #4. 设计表:外键
    #5. 新建查询
    #6. 建立表模型
    
    #注意:
    批量加注释:ctrl+?键
    批量去注释:ctrl+shift+?键

    练习题

    导出的sql语句代码

    /*
     数据导入:
     Navicat Premium Data Transfer
    
     Source Server         : localhost
     Source Server Type    : MySQL
     Source Server Version : 50624
     Source Host           : localhost
     Source Database       : sqlexam
    
     Target Server Type    : MySQL
     Target Server Version : 50624
     File Encoding         : utf-8
    
     Date: 10/21/2016 06:46:46 AM
    */
    
    SET NAMES utf8;
    SET FOREIGN_KEY_CHECKS = 0;
    
    -- ----------------------------
    --  Table structure for `class`
    -- ----------------------------
    DROP TABLE IF EXISTS `class`;
    CREATE TABLE `class` (
      `cid` int(11) NOT NULL AUTO_INCREMENT,
      `caption` varchar(32) NOT NULL,
      PRIMARY KEY (`cid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    --  Records of `class`
    -- ----------------------------
    BEGIN;
    INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
    COMMIT;
    
    -- ----------------------------
    --  Table structure for `course`
    -- ----------------------------
    DROP TABLE IF EXISTS `course`;
    CREATE TABLE `course` (
      `cid` int(11) NOT NULL AUTO_INCREMENT,
      `cname` varchar(32) NOT NULL,
      `teacher_id` int(11) NOT NULL,
      PRIMARY KEY (`cid`),
      KEY `fk_course_teacher` (`teacher_id`),
      CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    --  Records of `course`
    -- ----------------------------
    BEGIN;
    INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
    COMMIT;
    
    -- ----------------------------
    --  Table structure for `score`
    -- ----------------------------
    DROP TABLE IF EXISTS `score`;
    CREATE TABLE `score` (
      `sid` int(11) NOT NULL AUTO_INCREMENT,
      `student_id` int(11) NOT NULL,
      `course_id` int(11) NOT NULL,
      `num` int(11) NOT NULL,
      PRIMARY KEY (`sid`),
      KEY `fk_score_student` (`student_id`),
      KEY `fk_score_course` (`course_id`),
      CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
      CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    --  Records of `score`
    -- ----------------------------
    BEGIN;
    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');
    COMMIT;
    
    -- ----------------------------
    --  Table structure for `student`
    -- ----------------------------
    DROP TABLE IF EXISTS `student`;
    CREATE TABLE `student` (
      `sid` int(11) NOT NULL AUTO_INCREMENT,
      `gender` char(1) NOT NULL,
      `class_id` int(11) NOT NULL,
      `sname` varchar(32) NOT NULL,
      PRIMARY KEY (`sid`),
      KEY `fk_class` (`class_id`),
      CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    --  Records of `student`
    -- ----------------------------
    BEGIN;
    INSERT INTO `student` VALUES ('1', '', '1', '理解'), ('2', '', '1', '钢蛋'), ('3', '', '1', '张三'), ('4', '', '1', '张一'), ('5', '', '1', '张二'), ('6', '', '1', '张四'), ('7', '', '2', '铁锤'), ('8', '', '2', '李三'), ('9', '', '2', '李一'), ('10', '', '2', '李二'), ('11', '', '2', '李四'), ('12', '', '3', '如花'), ('13', '', '3', '刘三'), ('14', '', '3', '刘一'), ('15', '', '3', '刘二'), ('16', '', '3', '刘四');
    COMMIT;
    
    -- ----------------------------
    --  Table structure for `teacher`
    -- ----------------------------
    DROP TABLE IF EXISTS `teacher`;
    CREATE TABLE `teacher` (
      `tid` int(11) NOT NULL AUTO_INCREMENT,
      `tname` varchar(32) NOT NULL,
      PRIMARY KEY (`tid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    --  Records of `teacher`
    -- ----------------------------
    BEGIN;
    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');
    COMMIT;
    
    SET FOREIGN_KEY_CHECKS = 1;
    View Code

    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day4

    #准备表、记录  >>> 命令行
    mysql> create database db1;
    mysql> use db1;
    mysql> source /root/init.sql
    
    # navicat建表

    1,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

    快速建表

    #准备表、记录  >>> 命令行
    mysql> create database db1;
    mysql> use db1;
    mysql> source /root/init.sql
    
    # navicat建表

    练习题

    1、查询所有的课程的名称以及对应的任课老师姓名
    4、查询平均成绩大于八十分的同学的姓名和平均成绩
    7、 查询没有报李平老师课的学生姓名
    8、 查询没有同时选修物理课程和体育课程的学生姓名
    9、 查询挂科超过两门(包括两门)的学生姓名和班级
    # 参考答案
    #1、查询所有的课程的名称以及对应的任课老师姓名
    SELECT
        course.cname,
        teacher.tname
    FROM
        course
    INNER JOIN teacher ON course.teacher_id = teacher.tid;
    #4、查询平均成绩大于八十分的同学的姓名和平均成绩
    SELECT
        student.sname,
        t1.avg_num
    FROM
        student
    INNER JOIN (
        SELECT
            student_id,
            avg(num) AS avg_num
        FROM
            score
        GROUP BY
            student_id
        HAVING
            avg(num) > 80
    ) AS t1 ON student.sid = t1.student_id;
    #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)
    SELECT
        student.sname
    FROM
        student
    WHERE
        sid NOT IN (
            SELECT DISTINCT
                student_id
            FROM
                score
            WHERE
                course_id IN (
                    SELECT
                        course.cid
                    FROM
                        course
                    INNER JOIN teacher ON course.teacher_id = teacher.tid
                    WHERE
                        teacher.tname = '李平老师'
                )
        );
    #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)
    SELECT
        student.sname
    FROM
        student
    WHERE
        sid IN (
            SELECT
                student_id
            FROM
                score
            WHERE
                course_id IN (
                    SELECT
                        cid
                    FROM
                        course
                    WHERE
                        cname = '物理'
                    OR cname = '体育'
                )
            GROUP BY
                student_id
            HAVING
                COUNT(course_id) = 1
        );
    
    # 9、 查询挂科超过两门(包括两门)的学生姓名和班级
    select student.sname,class.caption from class INNER JOIN student
        on class.cid = student.class_id
        WHERE student.sid in 
        (select student_id from score where num < 60
        GROUP BY student_id
        HAVING COUNT(course_id) >=2)
        ;
    View Code

    pymysql模块

    # 1.安装:pip3 insatll pymysql
    
    # 2.代码链接
    import pymysql
    #链接
    conn=pymysql.connect(
      host='localhost',
      user='root',
      password='123',
      database='egon',
      charset='utf8')
    #游标
    cursor=conn.cursor() #执行完毕返回的结果集默认以元组显示
    #cursor=conn.cursor(cursor=pymysql.cursors.DictCursor)  # 以字典的方式显示数据
    
    # 3.pymysql操作数据库
    #执行sql语句
    user = input(">>>:").strip()
    pwd = input(">>>:").strip()
    sql='select * from userinfo where name="%s" and password="%s"' %(user,pwd) #注意%s需要加引号
    
    rows=cursor.execute(sql) #执行sql语句,返回sql查询成功的记录数目
    # 获取真实数据cursor.fetchone(),cursor.fetchall(),cursor.fetchmany(),类似管道取值,获取一条,所有,多条
    
    cursor.scroll(1,'relative')  # 相对移动
    cursor.scroll(3,'absolute')  # 绝对移动
    
    
    cursor.close()
    conn.close()
    View Code

    sql注入问题

    # 不要手动去拼接查询的sql语句
    username = input(">>>:").strip()
    password = input(">>>:").strip()
    sql = "select * from user where username='%s' and password='%s'"%(username,password)
    
    # 用户名正确
    username >>>: jason' -- jjsakfjjdkjjkjs
    # 用户名密码都不对的情况
    username >>>: xxx' or 1=1 --asdjkdklqwjdjkjasdljad
    password >>>: ''

    增删改,解决sql注入问题

    #
    sql = "insert into user(username,password) values(%s,%s)"
    rows = cursor.excute(sql,('jason','123'))
    
    # 修改
    sql = "update user set username='jasonDSB' where id=1"
    rows = cursor.excute(sql)
    
    """
    增和改单单执行excute并不会真正影响到数据,需要再执行conn.commit()才可以完成真正的增改
    """
    
    # 一次插入多行记录
    res = cursor,excutemany(sql,[(),(),()]
                            
     解决sql注入的问题                       
    import pymysql
    conn = pymysql.connect(
        host = '127.0.0.1', #ip地址
        port = 3306,        #默认端口号
        user = 'root',      # mysql账号
        password = '123',   #mysql密码
        database = 'day40', #mysql 库的名称
        charset = 'utf8' ,   #字符集打开的方式
        autocommit = True
    )
    cursor = conn.cursor(pymysql.cursors.DictCursor) #将查询的结果做成字典的格式
    res = cursor.execute('select * from userinfo') #execute 执行括号内的mql 语句 获得一个对象
    #对象内容是获取到的数据库内的ip个数
    print(res)
    # print(cursor.fetchmany())#取出数据将数据以列表的形式取出 但是只能取出一个
    # print(cursor.fetchall()) #取出一个字典形式的数据且是全部取出
    print(cursor.fetchone())
    # cursor.scroll(1,'relative') #光标移动 下一位
    print(cursor.fetchone())# 只能取出一个
    # cursor.scroll(1,"absolute") #光标移动到开始位置
    View Code
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  • 原文地址:https://www.cnblogs.com/yangxinpython/p/11400169.html
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