257 lines
9.1 KiB
Markdown
257 lines
9.1 KiB
Markdown
## 关系型数据入门
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### 关系型数据概述
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1. 数据持久化。
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2. 数据库发展史。
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3. 关系型数据库特点。
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- 理论基础：集合论和关系代数。
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- 具体表象：用二维表（有行和列）组织数据。
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- 编程语言：结构化查询语言（SQL）。
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4. E-R图。
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5. 关系型数据库产品。
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- Oracle
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- DB2
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- SQL Server
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- MySQL
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- SQLite
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### MySQL简介
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1. 安装和配置。
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2. 常用命令。
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### SQL详解
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1. DDL
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```SQL
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-- 如果存在SRS数据库就删除
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drop database if exists SRS;
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-- 创建学生选课系统数据库SRS并指定默认字符集为UTF8
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create database SRS default charset utf8;
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-- 切换至SRS数据库
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use SRS;
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-- 查看当前数据库中所有表
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show tables;
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-- 创建学生表TbStudent
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create table TbStudent
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(
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stuid integer not null,
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stuname varchar(20) not null,
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stusex bit default 1,
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stubirth datetime not null,
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stutel char(11),
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stuaddr varchar(255),
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stuphoto longblob,
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primary key (stuid)
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);
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-- 修改学生表删除stutel列
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alter table TbStudent drop column stutel;
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-- 查看学生表结构
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desc TbStudent;
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-- 如果表TbCourse已经存在就删除它
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drop table if exists TbCourse;
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-- 创建课程表TbCourse
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create table TbCourse
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(
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cosid integer not null,
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cosname varchar(50) not null,
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coscredit tinyint not null,
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cosintro varchar(255)
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);
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-- 给课程表设置主键约束
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alter table TbCourse add constraint pk_course primary key (cosid);
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-- 创建学生选课记录表TbSC
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create table TbSC
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(
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scid integer primary key auto_increment,
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sid integer not null,
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cid integer,
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scdate datetime not null,
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score float
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);
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-- 给表TbSC添加外键约束
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alter table TbSC add constraint fk_sid foreign key (sid) references TbStudent (stuid) on delete cascade on update cascade;
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alter table TbSC add constraint fk_cid foreign key (cid) references TBCourse (cosid);
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```
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2. DML
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```SQL
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-- 添加学生记录
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insert into TbStudent values (1001, '张三丰', default, '1978-1-1', '成都市一环路西二段17号', null);
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insert into TbStudent (stuid, stuname, stubirth) values (1002, '郭靖', '1980-2-2');
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insert into TbStudent (stuid, stuname, stusex, stubirth, stuaddr) values (1003, '黄蓉', 0, '1982-3-3', '成都市二环路南四段123号');
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insert into TbStudent values (1004, '张无忌', 1, '1990-4-4', null, null);
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insert into TbStudent values
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(1005, '丘处机', 1, '1983-5-5', '北京市海淀区宝盛北里西区28号', null),
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(1006, '王处一', 1, '1985-6-6', '深圳市宝安区宝安大道5010号', null),
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(1007, '刘处玄', 1, '1987-7-7', '郑州市金水区纬五路21号', null),
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(1008, '孙不二', 0, '1989-8-8', '武汉市光谷大道61号', null),
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(1009, '平一指', 1, '1992-9-9', '西安市雁塔区高新六路52号', null),
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(1010, '老不死', 1, '1993-10-10', '广州市天河区元岗路310号', null),
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(1011, '王大锤', 0, '1994-11-11', null, null),
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(1012, '隔壁老王', 1, '1995-12-12', null, null),
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(1013, '郭啸天', 1, '1977-10-25', null, null);
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-- 删除学生记录
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delete from TbStudent where stuid=1004;
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-- 更新学生记录
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update TbStudent set stubirth='1980-12-12', stuaddr='上海市宝山区同济支路199号' where stuid=1002;
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-- 添加课程记录
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insert into TbCourse values
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(1111, 'C语言程序设计', 3, '大神级讲师授课需要抢座'),
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(2222, 'Java程序设计', 3, null),
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(3333, '数据库概论', 2, null),
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(4444, '操作系统原理', 4, null);
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-- 添加学生选课记录
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insert into TbSC values
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(default, 1001, 1111, '2016-9-1', 95),
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(default, 1002, 1111, '2016-9-1', 94),
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(default, 1001, 2222, now(), null),
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(default, 1001, 3333, '2017-3-1', 85),
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(default, 1001, 4444, now(), null),
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(default, 1002, 4444, now(), null),
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(default, 1003, 2222, now(), null),
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(default, 1003, 3333, now(), null),
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(default, 1005, 2222, now(), null),
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(default, 1006, 1111, now(), null),
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(default, 1006, 2222, '2017-3-1', 80),
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(default, 1006, 3333, now(), null),
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(default, 1006, 4444, now(), null),
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(default, 1007, 1111, '2016-9-1', null),
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(default, 1007, 3333, now(), null),
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(default, 1007, 4444, now(), null),
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(default, 1008, 2222, now(), null),
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(default, 1010, 1111, now(), null);
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```
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3. DQL
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```SQL
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-- 查询所有学生信息
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select * from TbStudent;
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-- 查询所有课程名称及学分(投影和别名)
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select cosname as `课程名称`, coscredit as `学分` from TbCourse;
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-- 查询所有女学生的姓名和出生日期(筛选)
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select stuname, stubirth from TbStudent where stusex=0;
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-- 查询所有80后学生的姓名、性别和出生日期(筛选)
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select stuname as `姓名`, if(stusex, '男', '女') as `性别`, stubirth as `出生日期` from TbStudent where stubirth between '1980-1-1' and '1989-12-31';
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-- 查询姓王的学生姓名和性别(模糊)
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select stuname, stusex from TbStudent where stuname like '王%';
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-- 查询姓郭名字总共两个字的学生的姓名(模糊)
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select stuname from TbStudent where stuname like '郭_';
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-- 查询姓郭名字总共三个字的学生的姓名(模糊)
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select stuname from TbStudent where stuname like '郭__';
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-- 查询名字中有王字的学生的姓名(模糊)
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select stuname from TbStudent where stuname like '%王%';
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-- 查询没有录入家庭住址和照片的学生姓名(多条件筛选和空值处理)
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select stuname from TbStudent where stuaddr is null and stuphoto is null;
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-- 查询学生选课的所有日期(去重)
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select distinct scdate from TbSC;
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-- 查询学生的姓名和生日按年龄从大到小排列(排序)
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select stuname, stubirth from TbStudent order by stubirth;
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-- 查询所有录入了家庭住址的男学生的姓名、出生日期和家庭住址按年龄从小到大排列(多条件筛选和排序)
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select stuname, stubirth, stuaddr from TbStudent where stusex=1 and stuaddr is not null order by stubirth desc;
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-- 查询年龄最大的学生的出生日期(聚合函数)
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select min(stubirth) from TbStudent;
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-- 查询年龄最小的学生的出生日期(聚合函数)
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select max(stubirth) from TbStudent;
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-- 查询男女学生的人数(分组和聚合函数)
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select if(stusex, '男', '女') as `性别`, count(stusex) as `人数` from TbStudent group by stusex;
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-- 查询课程编号为1111的课程的平均成绩(筛选和聚合函数)
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select avg(score) as `平均成绩` from TbSC where cid=1111;
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-- 查询学号为1001的学生所有课程的总成绩(筛选和聚合函数)
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select sum(score) as `总成绩` from TbSC where sid=1001;
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-- 查询每个学生的学号和平均成绩, null值处理成0(分组和聚合函数)
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select sid as `学号`, ifnull(avg(score), 0) as `平均成绩` from TbSC group by sid;
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-- 查询平均成绩大于等于90分的学生的学号和平均成绩
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select sid as `学号`, avg(score) as `平均成绩` from TbSC group by sid having avg(score)>=90;
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-- 查询年龄最大的学生的姓名(子查询)
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select stuname from TbStudent where stubirth=(select min(stubirth) from TbStudent);
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-- 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
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select stuname from TbStudent where stuid in
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(select sid from TbSC group by sid having count(sid)>2);
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-- 查询选课学生的姓名和平均成绩(子查询和连接查询)
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-- 写法1:
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select stuname, avgscore from TbStudent t1 inner join
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(select sid, avg(score) as avgscore from TbSC where score is not null group by sid) t2 on t1.stuid=t2.sid;
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-- 写法2:
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select stuname, avgscore from TbStudent t1,
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(select sid, avg(score) as avgscore from TbSC where score is not null group by sid) t2 where t1.stuid=t2.sid;
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-- 查询学生姓名、所选课程名称和成绩(连接查询)
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-- 写法1:
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select stuname, cosname, score from
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TbStudent t1, TbCourse t2, TbSC t3
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where t1.stuid=t3.sid and t2.cosid=t3.cid and t3.score is not null;
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-- 写法2:
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select stuname, cosname, score from TbStudent t1 inner join TbCourse t2
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inner join (select sid, cid, score from TbSC where score is not null) t3
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on t1.stuid=t3.sid and t2.cosid=t3.cid;
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-- 查询每个学生的姓名和选课数量(左外连接和子查询)
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select stuname as `姓名`, ifnull(coscount, 0) as `选课数` from TbStudent t1
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left outer join (select sid, count(sid) as coscount from TbSC group by sid) t2 on t1.stuid=t2.sid;
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```
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4. DCL
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```SQL
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-- 创建名为hellokitty的用户
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create user 'hellokitty'@'localhost' identified by '123123';
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-- 将对SRS数据库所有对象的所有操作权限授予hellokitty
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grant all privileges on SRS.* to 'hellokitty'@'localhost';
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-- 召回hellokitty对SRS数据库所有对象的insert/delete/update权限
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revoke insert, delete, update on SRS.* from 'hellokitty'@'localhost';
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```
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### Python数据库编程
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1. MySQLdb
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2. PyMySQL
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