Navicat介绍及pymysql模块

内容回顾

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);

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', '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');
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;

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

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)
    ;

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()

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

# 增
sql = "insert into user(username,password) values(%s,%s)"
rows = cursor.(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,[(),(),()]

原文地址：https://www.cnblogs.com/yangyinyin/p/10878844.html