mysql入门
文章目录
- 1.登录数据库
- 2.如何查询数据库服务器中所有的数据库
- 3.创建数据库
- 4.如何选中某一个数据库进行操作
- 5.查询某个数据库中所有的数据表
- 6.如何创建一个数据表
- 7.查看是否创建成功
- 8.查看创建好的数据表的结构
- 9.如何往数据表中添加数据记录
- 10.查询数据表中的记录
- 11.mysql常用数据类型
- 12.删除数据
- 13.如何修改数据
- 14.总结常见数据记录
- 15.mysql建表的约束
- 15.1主键约束
- 15.2自增约束
- 15.3外键约束
- 15.4唯一约束
- 15.5非空约束
- 15.6默认约束
- 16.三大范式
- 16.1第一范式1NF
- 16.2第二范式2NF
- 16.3第三范式3NF
- 17.mysql查询练习
- 18.SQL的四种连接查询
- 18.1内连接 inner join 或者join
- 18.2外连接
- 18.2.1左连接 left join 或者 left outer join
- 18.2.2右连接 right join 或者 right outer join
- 18.2.3完全外连接 full join 或者 full outer join
- 19.mysql的事务
- 20.事务的四大特征ACID
- 20.1脏读(read uncommitted)
- 20.2不可重复读（read committed）
- 20.3可重复读（repeatable read）
- 20.4串行化（serializable）
- 20.5总结
b站链接
1.登录数据库
mysql -u root -p123456
2.如何查询数据库服务器中所有的数据库
show databases;
3.创建数据库
creat database test;
4.如何选中某一个数据库进行操作
mysql>use test;
Database changed
5.查询某个数据库中所有的数据表
mysql> show tables
6.如何创建一个数据表
mysql> CREATE TABLE pet(
-> name VARCHAR(20),
-> owner varchar(20),
-> species VARCHAR(20),
-> sex VARCHAR(1),
-> birth DATE,
-> death DATE);
Query OK, 0 rows affected (0.47 sec)
7.查看是否创建成功
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| pet |
+----------------+
1 row in set (0.00 sec)
8.查看创建好的数据表的结构
mysql> describe pet;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| owner | varchar(20) | YES | | NULL | |
| species | varchar(20) | YES | | NULL | |
| sex | varchar(1) | YES | | NULL | |
| birth | date | YES | | NULL | |
| death | date | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
9.如何往数据表中添加数据记录
mysql> insert into pet
-> values('puffball','Diane','hamster','f','1999-03-30',NULL);
Query OK, 1 row affected (1.11 sec)
mysql> insert into pet values('claws','Gwen','cat','m','1993-02-03',NULL);
Query OK, 1 row affected (1.13 sec)
mysql> insert into pet values('Buffy','Tim','dog','f','1997-02-05',NULL);
Query OK, 1 row affected (0.25 sec)
mysql> insert into pet values('Slim','Tom','tiger','m','2000-05-31',NULL);
Query OK, 1 row affected (0.25 sec)
mysql> select * from pet;
+----------+-----------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-----------+---------+------+------------+-------+
| puffball | Diane | hamster | f | 1999-03-30 | NULL |
| 旺财 | 周星驰 | 狗 | 公 | 1990-01-20 | NULL |
| claws | Gwen | cat | m | 1993-02-03 | NULL |
| Buffy | Tim | dog | f | 1997-02-05 | NULL |
| Slim | Tom | tiger | m | 2000-05-31 | NULL |
+----------+-----------+---------+------+------------+-------+
5 rows in set (0.00 sec)
10.查询数据表中的记录
mysql> select * from pet;
+----------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+-------+
| puffball | Diane | hamster | f | 1999-03-30 | NULL |
+----------+-------+---------+------+------------+-------+
1 row in set (0.00 sec)
mysql> insert into pet
-> values('旺财','周星驰','狗','公','1990-01-20',NULL);
Query OK, 1 row affected (0.16 sec)
mysql> select * from pet;
+----------+-----------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-----------+---------+------+------------+-------+
| puffball | Diane | hamster | f | 1999-03-30 | NULL |
| 旺财 | 周星驰 | 狗 | 公 | 1990-01-20 | NULL |
+----------+-----------+---------+------+------------+-------+
2 rows in set (0.00 sec)
11.mysql常用数据类型
整数类型：BIT、BOOL、TINY INT、SMALL INT、MEDIUM INT、 INT、 BIG INT
浮点数类型：FLOAT、DOUBLE、DECIMAL
字符串类型：CHAR、VARCHAR、TINY TEXT、TEXT、MEDIUM TEXT、LONGTEXT、TINY BLOB、BLOB、MEDIUM BLOB、LONG BLOB
日期类型：Date、DateTime、TimeStamp、Time、Year
其他数据类型：BINARY、VARBINARY、ENUM、SET、Geometry、Point、MultiPoint、LineString、MultiLineString、Polygon、GeometryCollection等
12.删除数据
mysql> delete from pet where name='Slim';
Query OK, 2 rows affected (1.06 sec)
mysql> select * from pet;
+----------+-----------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-----------+---------+------+------------+-------+
| puffball | Diane | hamster | f | 1999-03-30 | NULL |
| 旺财 | 周星驰 | 狗 | 公 | 1990-01-20 | NULL |
| claws | Gwen | cat | m | 1993-02-03 | NULL |
| Buffy | Tim | dog | f | 1997-02-05 | NULL |
+----------+-----------+---------+------+------------+-------+
4 rows in set (0.00 sec)
13.如何修改数据
mysql> update pet set name='汪汪' where owner='周星驰';
Query OK, 1 row affected (1.10 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from pet;
+----------+-----------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-----------+---------+------+------------+-------+
| puffball | Diane | hamster | f | 1999-03-30 | NULL |
| 汪汪 | 周星驰 | 狗 | 公 | 1990-01-20 | NULL |
| claws | Gwen | cat | m | 1993-02-03 | NULL |
| Buffy | Tim | dog | f | 1997-02-05 | NULL |
+----------+-----------+---------+------+------------+-------+
4 rows in set (0.00 sec)
14.总结常见数据记录
- 增加：insert
- 删除：delete
- 修改：update
- 查询：select
15.mysql建表的约束
15.1主键约束
它能够唯一确定一张表中的一条记录，也就是我们通过给某个字段添加约束，就可以使得字段不重复、不为空。
mysql> create table user(
-> id int primary key,
-> name varchar(20)
-> );
Query OK, 0 rows affected (2.20 sec)
mysql> describe user;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into user values(110,'张三');
Query OK, 1 row affected (0.17 sec)
mysql> insert into user values(110,'张三');
ERROR 1062 (23000): Duplicate entry '110' for key 'user.PRIMARY'
mysql> insert into user values(100,'张三');
Query OK, 1 row affected (1.08 sec)
mysql> select * from user;
+-----+--------+
| id | name |
+-----+--------+
| 100 | 张三 |
| 110 | 张三 |
+-----+--------+
2 rows in set (0.00 sec)
mysql> insert into user values(null,'张三');
ERROR 1048 (23000): Column 'id' cannot be null
mysql> insert into user values(1,null);
Query OK, 1 row affected (0.15 sec)
mysql> select * from user;
+-----+--------+
| id | name |
+-----+--------+
| 1 | NULL |
| 100 | 张三 |
| 110 | 张三 |
+-----+--------+
3 rows in set (0.00 sec)
--联合主键
--只要联合的主键值加起来不重复就可以了,但是任何一个字段不为空
mysql> create table user2(
-> id int,
-> name varchar(20),
-> passward varchar(20),
-> primary key(id,name)
-> );
Query OK, 0 rows affected (1.21 sec)
mysql> insert into user2 values(1,'zhangshan','123456');
Query OK, 1 row affected (1.06 sec)
mysql> insert into user2 values(1,'zhangshan','123456');
ERROR 1062 (23000): Duplicate entry '1-zhangshan' for key 'user2.PRIMARY'
mysql> insert into user2 values(1,'lisi','123456');
Query OK, 1 row affected (0.10 sec)
mysql> insert into user2 values(2,'zhangshan','123456');
Query OK, 1 row affected (1.08 sec)
mysql> select * from user2;
+----+-----------+----------+
| id | name | passward |
+----+-----------+----------+
| 1 | lisi | 123456 |
| 1 | zhangshan | 123456 |
| 2 | zhangshan | 123456 |
+----+-----------+----------+
3 rows in set (0.00 sec)
15.2自增约束
--auto_increment
mysql> create table user3(
-> id int primary key auto_increment,
-> name varchar(20));
Query OK, 0 rows affected (2.20 sec)
mysql> insert into user3 values(1,'xiaoming');
Query OK, 1 row affected (1.16 sec)
mysql> delete from user3 where id=1;
Query OK, 1 row affected (1.10 sec)
mysql> insert into user3 (name) values('xiaoming');
Query OK, 1 row affected (1.06 sec)
mysql> select * from user3;
+----+----------+
| id | name |
+----+----------+
| 2 | xiaoming |
| 3 | xiaoming |
+----+----------+
2 rows in set (0.00 sec)
如果我们创建表的时候，忘记创建主键约束了，该怎么办
mysql> create table user4
-> (
-> id int,
-> name varchar(20)
-> );
Query OK, 0 rows affected (2.01 sec)
mysql> describe user4;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
--修改表结构，添加主键
mysql> alter table user4 add primary key(id);
Query OK, 0 rows affected (2.60 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user4;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
--修改表结构，删除主键
mysql> alter table user4 drop primary key;
Query OK, 0 rows affected (2.66 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user4;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | NO | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
--使用modify修改字段，添加约束
mysql> alter table user4 modify id int primary key;
Query OK, 0 rows affected (2.27 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user4;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
15.3外键约束
涉及到两个表：父表、子表
主表、副表
--班级
create table classes
(
id int primary key,
name varchar(20)
);
--学生表
create table students
(
id int primary key,
name varchar(20),
class_id int,
foreign key(class_id) references classes(id)
)
mysql> desc classes;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> desc students;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
| class_id | int | YES | MUL | NULL | |
+----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
insert into classes values(1,'一班');
insert into classes values(2,'二班');
insert into classes values(3,'三班');
insert into classes values(4,'四班');
insert into students values(1001,'张三',1);
insert into students values(1002,'张三',2);
insert into students values(1003,'张三',3);
insert into students values(1004,'张三',4);
insert into students values(1005,'李四',5);
mysql> insert into students values(1005,'李四',5);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`test`.`students`, CONSTRAINT `students_ibfk_1` FOREIGN KEY (`class_id`) REFERENCES `classes` (`id`))
mysql> delete from classes where id=4;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`test`.`students`, CONSTRAINT `students_ibfk_1` FOREIGN KEY (`class_id`) REFERENCES `classes` (`id`))
--结论：
--1 主表classes中没有的数据值，在副表中，是不可以使用的；
--2 主表中的记录被副表引用，是不可以被删除的
15.4唯一约束
约束修饰的字段的值不可以重复
mysql> create table user5
-> (
-> id int,
-> name varchar(20)
-> );
Query OK, 0 rows affected (2.09 sec)
mysql> alter table user5 add unique(name);
Query OK, 0 rows affected (1.44 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user5;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into user5 values(1,'Json');
Query OK, 1 row affected (1.06 sec)
mysql> insert into user5 values(1,'Json');
ERROR 1062 (23000): Duplicate entry 'Json' for key 'user5.name'
mysql> insert into user5 values(1,'Lisi');
Query OK, 1 row affected (0.12 sec)
mysql> select * from user5;
+------+------+
| id | name |
+------+------+
| 1 | Json |
| 1 | Lisi |
+------+------+
2 rows in set (0.00 sec)
mysql> create table user6
-> (
-> id int,
-> name varchar(20),
-> unique(name)
-> );
Query OK, 0 rows affected (2.30 sec)
mysql> desc user6;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> create table user7
-> (
-> id int unique,
-> name varchar(20)
-> );
Query OK, 0 rows affected (2.51 sec)
mysql> desc user7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | UNI | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
--add unique() 添加唯一约束
mysql> alter table user7 add unique(name);
Query OK, 0 rows affected (0.71 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | UNI | NULL | |
| name | varchar(20) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into user7 values(1,'lisi');
Query OK, 1 row affected (1.06 sec)
mysql> insert into user7 values(1,'lisi');
ERROR 1062 (23000): Duplicate entry '1' for key 'user7.id'
mysql> insert into user7 values(2,'lisi');
ERROR 1062 (23000): Duplicate entry 'lisi' for key 'user7.name'
mysql> create table user8
-> ( id int,
-> name varchar(20),
-> unique(id,name)
-> );
Query OK, 0 rows affected (2.52 sec)
--unique(id,name)表示两个键在一起不重复就可以
mysql> desc user8;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | MUL | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into user8 values(1,'lisi');
Query OK, 1 row affected (0.10 sec)
mysql> insert into user8 values(1,'lisi');
ERROR 1062 (23000): Duplicate entry '1-lisi' for key 'user8.id'
mysql> insert into user8 values(2,'lisi');
Query OK, 1 row affected (0.09 sec)
mysql> select * from user8;
+------+------+
| id | name |
+------+------+
| 1 | lisi |
| 2 | lisi |
+------+------+
2 rows in set (0.00 sec)
如何删除唯一约束：
mysql> desc user7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | UNI | NULL | |
| name | varchar(20) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
--drop index 删除唯一约束
mysql> alter table user7 drop index id;
Query OK, 0 rows affected (1.48 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
--modify添加
mysql> alter table user7 modify id int unique;
Query OK, 0 rows affected (1.67 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | UNI | NULL | |
| name | varchar(20) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
总结：
1.建表的时候就添加约束
2.可以使用alter……add……
3.alter……modify……
4.删除 alter……drop index……
15.5非空约束
mysql> create table user9
-> (
-> id int,
-> name varchar(20) not null
-> );
Query OK, 0 rows affected (2.11 sec)
mysql> desc user9;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into user9 values(1,'zhangsan');
Query OK, 1 row affected (0.26 sec)
mysql> insert into user9 (id) values(2);
ERROR 1364 (HY000): Field 'name' doesn't have a default value
mysql> insert into user9 (name) values('lisi');
Query OK, 1 row affected (1.06 sec)
mysql> select * from user9;
+------+----------+
| id | name |
+------+----------+
| 1 | zhangsan |
| NULL | lisi |
+------+----------+
2 rows in set (0.00 sec)
15.6默认约束
当我们插入字段的时候，如果没有传值，就会使用默认值
mysql> create table user10(
-> id int,
-> name varchar(20),
-> age int default 10
-> );
Query OK, 0 rows affected (2.13 sec)
mysql> desc user10;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| age | int | YES | | 10 | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> insert into user10 (id,name) values (1,'zhangsan');
Query OK, 1 row affected (1.06 sec)
mysql> select * from user10;
+------+----------+------+
| id | name | age |
+------+----------+------+
| 1 | zhangsan | 10 |
+------+----------+------+
1 row in set (0.00 sec)
mysql> insert into user10 values(1,'zhangsan',20);
Query OK, 1 row affected (1.07 sec)
mysql> select * from user10;
+------+----------+------+
| id | name | age |
+------+----------+------+
| 1 | zhangsan | 10 |
| 1 | zhangsan | 20 |
+------+----------+------+
2 rows in set (0.00 sec)
16.三大范式
16.1第一范式1NF
数据表中所有字段都是不可分割的原子值
create table student2(
id int primary key,
name varchar(20),
address varchar(30)
);
insert into student2 values(1,'张三','安徽铜陵1号');
insert into student2 values(2,'李四','安徽铜陵2号');
insert into student2 values(3,'王五','安徽铜陵3号');
create table student3(
id int primary key,
name varchar(20),
privince varchar(30),
city varchar(30),
number varchar(20)
);
insert into student3 values(1,'张三','安徽','铜陵','1号');
insert into student3 values(2,'李四','安徽','铜陵','2号');
insert into student3 values(3,'王五','安徽','铜陵','3号');
--address字段值还可以继续拆分，就不能满足1NF
--范式设计的越详细，对于某些实际的操作可能更好，但是不一定不是绝对好
16.2第二范式2NF
- 必须是满足第一范式的前提下，第二范式要求，除主键外的每一列都必须完全依赖于主键
- 如果出现不完全依赖，只可能发生在联合主键的情况下
create table myorder(
product_id int,
customer_id int,
product_name varchar(20),
customer_name varchar(20),
primary key(product_id,customer_id)
);
--问题：
--除主键以外的其他列，只依赖与主键的部分字段
--拆表
create table myorder(
order_id int primary key,
product_id int,
customer_id int,
);
create table product(
id int primary key,
name varchar(20)
);
create table customer(
id int primary key,
name varchar(20)
);
16.3第三范式3NF
必须先满足第二范式，除开主键列的其他列之间不能有传递依赖
create table myorder(
order_id int primary key,
product_id int,
customer_id int,
customer_phone varchar(15)
);
--customer_phone除了依赖主键，还可能依赖customer_id
--修改：
create table myorder(
order_id int primary key,
product_id int,
customer_id int
);
create table customer(
id int primary key,
name varchar(20),
customer_phone varchar(15)
);
17.mysql查询练习
| 学生表Student | 课程表Course | 成绩表Score | 教师表Teacher |
|---|---|---|---|
| 学号 sno | 课程号 cno | 学号sno | 教师编号tno |
| 姓名 sname | 课程名cname | 课程号cno | 教师名字tname |
| 出生年月日 | 教师编号 | 成绩 | 教师性别 |
| 所在班级 | 出生年月日 | ||
| 职称 | |||
| 所在部门 |
--建表
create table Student
(
sno varchar(20) primary key,
sname varchar(20) not null,
ssex varchar(10) not null,
sbirthday datetime,
class varchar(20)
);
create table Teacher
(
tno varchar(20) primary key,
tname varchar(20) not null,
tsex varchar(10) not null,
tbirthday datetime,
prof varchar(20) not null,
depart varchar(20) not null
);
create table Course
(
cno varchar(20) primary key,
cname varchar(20) not null,
tno varchar(20) not null,
foreign key(tno) references Teacher(tno)
);
create table Score(
sno varchar(20) not null,
cno varchar(20) not null,
degree decimal,
foreign key(sno) references Student(sno),
foreign key(cno) references Course(cno),
primary key(sno,cno)
);
--添加数据
#添加学生表数据
insert into student values('108','曾华','男','1977-09-01','95033');
insert into student values('105','匡明','男','1975-10-02','95031');
insert into student values('107','王丽','女','1976-01-23','95033');
insert into student values('101','李军','男','1976-02-20','95033');
insert into student values('109','王芳','女','1975-02-10','95031');
insert into student values('103','陆君','男','1974-06-03','95031');
insert into student values('102','哈桑','男','1974-06-03','95031');
insert into student values('104','金闪闪','男','1974-06-03','95031');
insert into student values('106','卫宫','男','1974-06-03','95031');
#添加教师数据
insert into teacher values('804','李诚','男','1974-06-03','副教授','计算机系');
insert into teacher values('856','张旭','男','1975-06-03','讲师','电子信息系');
insert into teacher values('825','王萍','女','1956-06-03','助教','计算机系');
insert into teacher values('831','刘冰','女','1977-06-23','助教','电子信息系');
#添加课程表
insert into course values('3-105','计算机导论','825');
insert into course values('3-245','操作系统','804');
insert into course values('6-166','数字电路','856');
insert into course values('9-888','高等数学','831');
#添加成绩表
insert into score values('103','3-245','86');
insert into score values('105','3-245','75');
insert into score values('109','3-245','68');
insert into score values('103','3-105','92');
insert into score values('105','3-105','88');
insert into score values('109','3-105','76');
insert into score values('103','6-166','85');
insert into score values('105','6-166','79');
insert into score values('109','6-166','81');
--查询练习
--1.查询student表中所有记录的sname，ssex，和class列
mysql> select sname,ssex,class from student;
+-----------+------+-------+
| sname | ssex | class |
+-----------+------+-------+
| 李军 | 男 | 95033 |
| 哈桑 | 男 | 95031 |
| 陆君 | 男 | 95031 |
| 金闪闪 | 男 | 95031 |
| 匡明 | 男 | 95031 |
| 卫宫 | 男 | 95031 |
| 王丽 | 女 | 95033 |
| 曾华 | 男 | 95033 |
| 王芳 | 女 | 95031 |
+-----------+------+-------+
9 rows in set (0.00 sec)
--2.查询教师表不重复的depart列
mysql> select distinct depart from teacher;
+-----------------+
| depart |
+-----------------+
| 计算机系 |
| 电子信息系 |
+-----------------+
2 rows in set (0.04 sec)
--3.查询score表中成绩在60-80之间的所有记录
--between and 包含边界值
mysql> select * from score where degree between 60 and 80;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
+-----+-------+--------+
4 rows in set (0.02 sec)
mysql> select * from score where degree > 60 and degree < 80;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
+-----+-------+--------+
4 rows in set (0.85 sec)
--4.查询score表中成绩为85、86或者88的记录
mysql> select * from score where degree in (85,86,88);
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 105 | 3-105 | 88 |
+-----+-------+--------+
3 rows in set (0.00 sec)
--5.查询student表中“95031”班或者性别为“女”的同学记录
mysql> select * from student where class='95031' or ssex='女';
+-----+-----------+------+---------------------+-------+
| sno | sname | ssex | sbirthday | class |
+-----+-----------+------+---------------------+-------+
| 102 | 哈桑 | 男 | 1974-06-03 00:00:00 | 95031 |
| 103 | 陆君 | 男 | 1974-06-03 00:00:00 | 95031 |
| 104 | 金闪闪 | 男 | 1974-06-03 00:00:00 | 95031 |
| 105 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 106 | 卫宫 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 109 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
+-----+-----------+------+---------------------+-------+
7 rows in set (0.00 sec)
--6.以class降序查询student表中所有记录
mysql> select * from student order by class desc;
+-----+-----------+------+---------------------+-------+
| sno | sname | ssex | sbirthday | class |
+-----+-----------+------+---------------------+-------+
| 101 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 108 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 哈桑 | 男 | 1974-06-03 00:00:00 | 95031 |
| 103 | 陆君 | 男 | 1974-06-03 00:00:00 | 95031 |
| 104 | 金闪闪 | 男 | 1974-06-03 00:00:00 | 95031 |
| 105 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 106 | 卫宫 | 男 | 1974-06-03 00:00:00 | 95031 |
| 109 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
+-----+-----------+------+---------------------+-------+
9 rows in set (0.00 sec)
--7.以cno升序、degree降序查询score表中的所有记录
mysql> select * from score order by cno asc,degree desc;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-105 | 92 |
| 105 | 3-105 | 88 |
| 109 | 3-105 | 76 |
| 103 | 3-245 | 86 |
| 105 | 3-245 | 75 |
| 109 | 3-245 | 68 |
| 103 | 6-166 | 85 |
| 109 | 6-166 | 81 |
| 105 | 6-166 | 79 |
+-----+-------+--------+
9 rows in set (0.00 sec)
--8.查询“95031”班的学生人数
--统计 count
mysql> select count(*) from student where class='95031';
+----------+
| count(*) |
+----------+
| 6 |
+----------+
1 row in set (0.04 sec)
--9.查询score表中最高分的学生学号和课程号（子查询或者排序）
mysql> select sno,cno from score where degree=(select max(degree) from score);
+-----+-------+
| sno | cno |
+-----+-------+
| 103 | 3-105 |
+-----+-------+
1 row in set (0.06 sec)
步骤：
1.找到最高分
select max(degree) from score;
2.找最高分的sno,cno
select sno,cno from score where degree=(select max(degree) from score);
--排序的做法
mysql> select sno,cno,degree from score order by degree;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 109 | 3-245 | 68 |
| 105 | 3-245 | 75 |
| 109 | 3-105 | 76 |
| 105 | 6-166 | 79 |
| 109 | 6-166 | 81 |
| 103 | 6-166 | 85 |
| 103 | 3-245 | 86 |
| 105 | 3-105 | 88 |
| 103 | 3-105 | 92 |
+-----+-------+--------+
9 rows in set (0.00 sec)
mysql> select sno,cno,degree from score order by degree desc limit 0,1;
--limit x,y x表示开始下标，y表示查询数目
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-105 | 92 |
+-----+-------+--------+
1 row in set (0.02 sec)
--10.查询每门课的平均成绩
--avg()
--查询一门课
mysql> select avg(degree) from score where cno='3-105';
+-------------+
| avg(degree) |
+-------------+
| 85.3333 |
+-------------+
1 row in set (0.04 sec)
--查询每门课
--group by 分组
mysql> select cno,avg(degree) from score group by cno;
+-------+-------------+
| cno | avg(degree) |
+-------+-------------+
| 3-105 | 85.3333 |
| 3-245 | 76.3333 |
| 6-166 | 81.6667 |
+-------+-------------+
3 rows in set (0.00 sec)
--11.查询score表中至少有2名同学选修的并以3开头的课程的平均分数
select cno,avg(degree) from score
group by cno
having count(sno)>=2 and cno like '3%';
mysql> select cno,avg(degree) from score group by cno
-> having count(sno)>=2 and cno like '3%';
+-------+-------------+
| cno | avg(degree) |
+-------+-------------+
| 3-105 | 85.3333 |
| 3-245 | 76.3333 |
+-------+-------------+
2 rows in set (0.07 sec)
| 学生表Student | 课程表Course | 成绩表Score | 教师表Teacher |
|---|---|---|---|
| 学号 sno | 课程号 cno | 学号sno | 教师编号tno |
| 姓名 sname | 课程名cname | 课程号cno | 教师名字tname |
| 出生年月日sbirthday | 教师编号tno | 成绩degree | 教师性别tsex |
| 所在班级 | 出生年月日 | ||
| 职称 | |||
| 所在部门 |
--多表查询
--12.查询所有学生的sname,cno和degree列
mysql> select sname,cno,degree from student,score
-> where student.sno=score.sno;
+--------+-------+--------+
| sname | cno | degree |
+--------+-------+--------+
| 陆君 | 3-105 | 92 |
| 陆君 | 3-245 | 86 |
| 陆君 | 6-166 | 85 |
| 匡明 | 3-105 | 88 |
| 匡明 | 3-245 | 75 |
| 匡明 | 6-166 | 79 |
| 王芳 | 3-105 | 76 |
| 王芳 | 3-245 | 68 |
| 王芳 | 6-166 | 81 |
+--------+-------+--------+
9 rows in set (0.00 sec)
--13.查询所有学生的sname,cname和degree列
mysql> select sname,cname,degree from student,course,score
-> where student.sno=score.sno and course.cno=score.cno;
+--------+-----------------+--------+
| sname | cname | degree |
+--------+-----------------+--------+
| 陆君 | 计算机导论 | 92 |
| 陆君 | 操作系统 | 86 |
| 陆君 | 数字电路 | 85 |
| 匡明 | 计算机导论 | 88 |
| 匡明 | 操作系统 | 75 |
| 匡明 | 数字电路 | 79 |
| 王芳 | 计算机导论 | 76 |
| 王芳 | 操作系统 | 68 |
| 王芳 | 数字电路 | 81 |
+--------+-----------------+--------+
9 rows in set (0.00 sec)
mysql> select sname,cname,degree,student.sno,course.cno from student,course,score
-> where student.sno=score.sno and course.cno=score.cno;
+--------+-----------------+--------+-----+-------+
| sname | cname | degree | sno | cno |
+--------+-----------------+--------+-----+-------+
| 陆君 | 计算机导论 | 92 | 103 | 3-105 |
| 陆君 | 操作系统 | 86 | 103 | 3-245 |
| 陆君 | 数字电路 | 85 | 103 | 6-166 |
| 匡明 | 计算机导论 | 88 | 105 | 3-105 |
| 匡明 | 操作系统 | 75 | 105 | 3-245 |
| 匡明 | 数字电路 | 79 | 105 | 6-166 |
| 王芳 | 计算机导论 | 76 | 109 | 3-105 |
| 王芳 | 操作系统 | 68 | 109 | 3-245 |
| 王芳 | 数字电路 | 81 | 109 | 6-166 |
+--------+-----------------+--------+-----+-------+
9 rows in set (0.00 sec)
mysql> select sname,cname,degree,student.sno,student.sno as stu_sno,course.cno,course.cno as cou_cno from student,course,score
-> where student.sno=score.sno and course.cno=score.cno;
+--------+-----------------+--------+-----+---------+-------+---------+
| sname | cname | degree | sno | stu_sno | cno | cou_cno |
+--------+-----------------+--------+-----+---------+-------+---------+
| 陆君 | 计算机导论 | 92 | 103 | 103 | 3-105 | 3-105 |
| 陆君 | 操作系统 | 86 | 103 | 103 | 3-245 | 3-245 |
| 陆君 | 数字电路 | 85 | 103 | 103 | 6-166 | 6-166 |
| 匡明 | 计算机导论 | 88 | 105 | 105 | 3-105 | 3-105 |
| 匡明 | 操作系统 | 75 | 105 | 105 | 3-245 | 3-245 |
| 匡明 | 数字电路 | 79 | 105 | 105 | 6-166 | 6-166 |
| 王芳 | 计算机导论 | 76 | 109 | 109 | 3-105 | 3-105 |
| 王芳 | 操作系统 | 68 | 109 | 109 | 3-245 | 3-245 |
| 王芳 | 数字电路 | 81 | 109 | 109 | 6-166 | 6-166 |
+--------+-----------------+--------+-----+---------+-------+---------+
9 rows in set (0.00 sec)
--14.查询“95031“班学生的每门课的平均分
select * from score where sno in (select sno from student where class='95031')
mysql> select * from score where sno in (select sno from student where class='95031');
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
9 rows in set (0.00 sec)
select cno,avg(degree) from score where sno in (select sno from student where class='95031') group by cno;
mysql> select cno,avg(degree) from score where sno in (select sno from student where class='95031') group by cno;
+-------+-------------+
| cno | avg(degree) |
+-------+-------------+
| 3-105 | 85.3333 |
| 3-245 | 76.3333 |
| 6-166 | 81.6667 |
+-------+-------------+
3 rows in set (0.84 sec)
--15.查询选修”3-105“课程的成绩高于”109“号同学”3-105“成绩的所有同学的记录
mysql> select degree from score
-> where sno='109' and cno='3-105';
+--------+
| degree |
+--------+
| 76 |
+--------+
1 row in set (0.00 sec)
mysql> select * from score where degree>(select degree from score where sno='109' and cno='3-105') and cno='3-105'
-> ;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-105 | 92 |
| 105 | 3-105 | 88 |
+-----+-------+--------+
2 rows in set (0.00 sec)
--16.查询成绩高于学号为”109“、课程号为”3-105“的成绩的所以记录
mysql> select * from score where degree>(select degree from score where sno='109' and cno='3-105');
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 105 | 3-105 | 88 |
| 105 | 6-166 | 79 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
6 rows in set (0.00 sec)
--17.查询和学号为108、101的同学同年出生的所有学生的sno,sname和sbirthday列
select year(sbirthday) from student where sno in (101,108);
select * from student where year(sbirthday) in(select year(sbirthday) from student where sno in (101,108));
mysql> select * from student where year(sbirthday) in(select year(sbirthday) from student where sno in (101,108));
+-----+--------+------+---------------------+-------+
| sno | sname | ssex | sbirthday | class |
+-----+--------+------+---------------------+-------+
| 101 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 108 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
+-----+--------+------+---------------------+-------+
3 rows in set (0.02 sec)
--18.查询”张旭“教师任课的学生成绩
--根据表的关联
mysql> select sno,score.cno,degree from score,course,teacher
-> where tname='张旭' and teacher.tno=course.tno
-> and course.cno=score.cno;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 6-166 | 85 |
| 105 | 6-166 | 79 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
3 rows in set (0.00 sec)
--三层嵌套
mysql> select * from score where cno=(select cno from course where tno=(select tno from teacher where tname='张旭'));
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 6-166 | 85 |
| 105 | 6-166 | 79 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
3 rows in set (0.00 sec)
--19.查询选修某课程的同学多于5人的教师姓名
insert into score values('101','3-105','90');
insert into score values('102','3-105','91');
insert into score values('104','3-105','89');
mysql> select tname from teacher where tno=(select tno from course where cno=(select cno from score group by cno having count(cno)>5));
+--------+
| tname |
+--------+
| 王萍 |
+--------+
1 row in set (0.00 sec)
--20.查询95033班和95031班全体学生的记录
mysql> insert into student values('110','张飞','男','1977-02-01','95038');
Query OK, 1 row affected (0.11 sec)
select * from student where class in ('95033','95031');
--21.查询“计算机系”与“电子工程系”不同制成的教师的tname和prof
--union求并集
mysql> select * from teacher where depart='计算机系' and prof not in(select prof from teacher where depart='电子信息系')
-> union select * from teacher where depart='电子信息系' and prof not in(select prof from teacher where depart='计算机系');
+-----+--------+------+---------------------+-----------+-----------------+
| tno | tname | tsex | tbirthday | prof | depart |
+-----+--------+------+---------------------+-----------+-----------------+
| 804 | 李诚 | 男 | 1974-06-03 00:00:00 | 副教授 | 计算机系 |
| 856 | 张旭 | 男 | 1975-06-03 00:00:00 | 讲师 | 电子信息系 |
+-----+--------+------+---------------------+-----------+-----------------+
2 rows in set (0.00 sec)
--22.查询选修编号为3-105课程且成绩至少高于选修编号为3-245的同学的cno,sno和degree,
--并将degree降序排序
--至少？ 即大于其中任意一个 any
mysql> select * from score
-> where cno='3-105' and degree> any(select degree from score where cno='3-245')
-> order by degree desc;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 103 | 3-105 | 92 |
| 102 | 3-105 | 91 |
| 101 | 3-105 | 90 |
| 104 | 3-105 | 89 |
| 105 | 3-105 | 88 |
| 109 | 3-105 | 76 |
+-----+-------+--------+
6 rows in set (0.00 sec)
--23.查询选修编号为3-105且成绩高于选修编号为3-245课程的同学cno,sno和degree
mysql> select * from score
-> where cno='3-105' and degree> all(select degree from score where cno='3-245');
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 90 |
| 102 | 3-105 | 91 |
| 103 | 3-105 | 92 |
| 104 | 3-105 | 89 |
| 105 | 3-105 | 88 |
+-----+-------+--------+
5 rows in set (0.00 sec)
mysql> select * from score
-> where cno='3-105' and degree>(select max(degree) from score where cno='3-245');
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 90 |
| 102 | 3-105 | 91 |
| 103 | 3-105 | 92 |
| 104 | 3-105 | 89 |
| 105 | 3-105 | 88 |
+-----+-------+--------+
5 rows in set (0.00 sec)
--23.查询所有教师和同学的name,sex,birthday
mysql> select sname,ssex,sbirthday from student
-> union
-> select tname,tsex,tbirthday from teacher;
+-----------+------+---------------------+
| sname | ssex | sbirthday |
+-----------+------+---------------------+
| 李军 | 男 | 1976-02-20 00:00:00 |
| 哈桑 | 男 | 1974-06-03 00:00:00 |
| 陆君 | 男 | 1974-06-03 00:00:00 |
| 金闪闪 | 男 | 1974-06-03 00:00:00 |
| 匡明 | 男 | 1975-10-02 00:00:00 |
| 卫宫 | 男 | 1974-06-03 00:00:00 |
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 曾华 | 男 | 1977-09-01 00:00:00 |
| 王芳 | 女 | 1975-02-10 00:00:00 |
| 张飞 | 男 | 1977-02-01 00:00:00 |
| 李诚 | 男 | 1974-06-03 00:00:00 |
| 王萍 | 女 | 1956-06-03 00:00:00 |
| 刘冰 | 女 | 1977-06-23 00:00:00 |
| 张旭 | 男 | 1975-06-03 00:00:00 |
+-----------+------+---------------------+
14 rows in set (0.00 sec)
mysql> select sname as name,ssex as sex,sbirthday as birthday from student
-> union
-> select tname,tsex,tbirthday from teacher;
+-----------+-----+---------------------+
| name | sex | birthday |
+-----------+-----+---------------------+
| 李军 | 男 | 1976-02-20 00:00:00 |
| 哈桑 | 男 | 1974-06-03 00:00:00 |
| 陆君 | 男 | 1974-06-03 00:00:00 |
| 金闪闪 | 男 | 1974-06-03 00:00:00 |
| 匡明 | 男 | 1975-10-02 00:00:00 |
| 卫宫 | 男 | 1974-06-03 00:00:00 |
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 曾华 | 男 | 1977-09-01 00:00:00 |
| 王芳 | 女 | 1975-02-10 00:00:00 |
| 张飞 | 男 | 1977-02-01 00:00:00 |
| 李诚 | 男 | 1974-06-03 00:00:00 |
| 王萍 | 女 | 1956-06-03 00:00:00 |
| 刘冰 | 女 | 1977-06-23 00:00:00 |
| 张旭 | 男 | 1975-06-03 00:00:00 |
+-----------+-----+---------------------+
14 rows in set (0.00 sec)
--24.查询所有女教师和女同学的name,sex,birthday
mysql> select sname as name,ssex as sex,sbirthday as birthday from student where ssex='女'
-> union
-> select tname,tsex,tbirthday from teacher where tsex='女';
+--------+-----+---------------------+
| name | sex | birthday |
+--------+-----+---------------------+
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 王芳 | 女 | 1975-02-10 00:00:00 |
| 王萍 | 女 | 1956-06-03 00:00:00 |
| 刘冰 | 女 | 1977-06-23 00:00:00 |
+--------+-----+---------------------+
4 rows in set (0.00 sec)
--25.查询成绩比该课程平均成绩低的同学的成绩表
mysql> select cno,avg(degree) from score group by cno;
+-------+-------------+
| cno | avg(degree) |
+-------+-------------+
| 3-105 | 87.6667 |
| 3-245 | 76.3333 |
| 6-166 | 81.6667 |
+-------+-------------+
3 rows in set (0.00 sec)
mysql> select * from score;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 90 |
| 102 | 3-105 | 91 |
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 104 | 3-105 | 89 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
12 rows in set (0.00 sec)
mysql> select * from score as a where degree <(select avg(degree) from score as b where a.cno=b.cno);
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
5 rows in set (0.00 sec)
--26.查询至少有2名男生的班级号
mysql> select class from student where ssex='男' group by class having count(class )>=2;
+-------+
| class |
+-------+
| 95033 |
| 95031 |
+-------+
2 rows in set (0.00 sec)
--27.查询student表中每个学生的姓名和年龄
--年龄=当前年份-出生年份 sage=year(now())-year(sbirthday)
mysql> select sname,year(now())-year(sbirthday) as sage from student;
+-----------+------+
| sname | sage |
+-----------+------+
| 李军 | 44 |
| 哈桑 | 46 |
| 陆君 | 46 |
| 金闪闪 | 46 |
| 匡明 | 45 |
| 卫宫 | 46 |
| 王丽 | 44 |
| 曾华 | 43 |
| 王芳 | 45 |
| 张飞 | 43 |
+-----------+------+
10 rows in set (0.00 sec)
--28.查询男教师及其所上的课程
mysql> select * from course where tno in (select tno from teacher where tsex='男');
+-------+--------------+-----+
| cno | cname | tno |
+-------+--------------+-----+
| 3-245 | 操作系统 | 804 |
| 6-166 | 数字电路 | 856 |
+-------+--------------+-----+
2 rows in set (0.00 sec)
--29.假设建了一个grade表
mysql> create table grade
-> (
-> low int(3),
-> upp int(3),
-> grade char(1)
-> );
Query OK, 0 rows affected, 2 warnings (1.33 sec)
insert into grade values(90,100,'A');
insert into grade values(80,89,'B');
insert into grade values(70,79,'C');
insert into grade values(60,69,'D');
insert into grade values(50,59,'E');
--查询所有学生的sno,cno和grade列
mysql> select sno,cno,grade from score,grade where degree between low and upp;
+-----+-------+-------+
| sno | cno | grade |
+-----+-------+-------+
| 101 | 3-105 | A |
| 102 | 3-105 | A |
| 103 | 3-105 | A |
| 103 | 3-245 | B |
| 103 | 6-166 | B |
| 104 | 3-105 | B |
| 105 | 3-105 | B |
| 105 | 3-245 | C |
| 105 | 6-166 | C |
| 109 | 3-105 | C |
| 109 | 3-245 | D |
| 109 | 6-166 | B |
+-----+-------+-------+
12 rows in set (0.00 sec)
18.SQL的四种连接查询
--创建两个表：
--person: id name cardId
--card: id name
create table person
(
id int,
name varchar(20),
cardId int
);
create table card
(
id int,
name varchar(20)
);
insert into card values(1,'饭卡');
insert into card values(2,'建行卡');
insert into card values(3,'农行卡');
insert into card values(4,'工商卡');
insert into card values(5,'邮政卡');
insert into person values(1,'张三',1);
insert into person values(2,'李四',3);
insert into person values(3,'王五',6);
--没有创建外键
18.1内连接 inner join 或者join
--inner join查询
mysql> select * from person inner join card on person.cardid=card.id;
+------+--------+--------+------+-----------+
| id | name | cardId | id | name |
+------+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
+------+--------+--------+------+-----------+
2 rows in set (0.00 sec)
--内连接就是两张表中的数据，通过某个字段相对，查询出相关记录数据
select * from person join card on person.cardid=card.id;
18.2外连接
18.2.1左连接 left join 或者 left outer join
mysql> select * from person left join card on person.cardid=card.id;
+------+--------+--------+------+-----------+
| id | name | cardId | id | name |
+------+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| 3 | 王五 | 6 | NULL | NULL |
+------+--------+--------+------+-----------+
3 rows in set (0.00 sec)
--左外连接，会把左边的表里面的所有数据取出来，而右边表中的数据，如果有相等的，就显示出来
--如果没有，就会补充NULL
select * from person left outer join card on person.cardid=card.id;
18.2.2右连接 right join 或者 right outer join
mysql> select * from person right join card on person.cardid=card.id;
+------+--------+--------+------+-----------+
| id | name | cardId | id | name |
+------+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| NULL | NULL | NULL | 2 | 建行卡 |
| NULL | NULL | NULL | 4 | 工商卡 |
| NULL | NULL | NULL | 5 | 邮政卡 |
+------+--------+--------+------+-----------+
5 rows in set (0.00 sec)
--右外连接，会把右边的表里面的所有数据取出来，而左边表中的数据，如果有相等的，就显示出来
--如果没有，就会补充NULL
select * from person right outer join card on person.cardid=card.id;
18.2.3完全外连接 full join 或者 full outer join
select * from person full join card on person.cardid=card.id;
--mysql不支持 full join
--可以使用union实现 full join
mysql> select * from person left join card on person.cardid=card.id
-> union
-> select * from person right join card on person.cardid=card.id;
+------+--------+--------+------+-----------+
| id | name | cardId | id | name |
+------+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| 3 | 王五 | 6 | NULL | NULL |
| NULL | NULL | NULL | 2 | 建行卡 |
| NULL | NULL | NULL | 4 | 工商卡 |
| NULL | NULL | NULL | 5 | 邮政卡 |
+------+--------+--------+------+-----------+
6 rows in set (0.00 sec)
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-0zoWYTwA-1584546516889)(C:\Users\严高飞\AppData\Roaming\Typora\typora-user-images\1584534397110.png)]
19.mysql的事务
--mysql中，事务是一个最小的不可分割的工作单元，事务能够保证一个业务的完整性
--比如：银行转账
a->b -100
update user set money=money-100 where name='a';
b-> +100
update user set money=money+100 where name='b';
--实际的程序中，如果只有一条语句执行成功了，而另一条语句没有执行成功？
--出现数据前后的不一致。
update user set money=money-100 where name='a';
update user set money=money+100 where name='b';
--多条sql语句可能会有同时成功的要求，要么就同时失败
--mysql中如何控制事务？
1.默认开启事务（自动提交）
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
| 1 |
+--------------+
1 row in set (0.00 sec)
--默认事务开启的作用？
--当我们去执行一个sql语句时，效果会立即体现出来，且不能回滚。
create database bank;
create table user
(
id int primary key,
name varchar(20),
money int
);
insert into user values(1,'tom',1000);
--事务回滚，撤销sql语句的运行效果
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | tom | 1000 |
+----+------+-------+
1 row in set (0.00 sec)
--设置mysql 自动提交为false
set autocommit=0;
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
| 0 |
+--------------+
1 row in set (0.00 sec)
--上面的操作，关闭了mysql的自动提交（commit）
insert into user values(2,'jack',1000);
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | tom | 1000 |
| 2 | jack | 1000 |
+----+------+-------+
2 rows in set (0.00 sec)
mysql> rollback;
Query OK, 0 rows affected (0.91 sec)
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | tom | 1000 |
+----+------+-------+
1 row in set (0.00 sec)
mysql> insert into user values(2,'jack',1000);
Query OK, 1 row affected (0.00 sec)
--手动提交（持久性）
mysql> commit;
Query OK, 0 rows affected (0.14 sec)
--此时rollback失效
--自动提交 @@autocommit=1
--手动提交 commit;
--手动回滚 rollback;
--转账：
mysql> update user set money=money-100 where name='tom';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> update user set money=money+100 where name='jack';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
+----+------+-------+
2 rows in set (0.00 sec)
mysql> rollback;
Query OK, 0 rows affected (0.03 sec)
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | tom | 1000 |
| 2 | jack | 1000 |
+----+------+-------+
2 rows in set (0.00 sec)
--事务给我们提供了一个返回的机会
20.事务的四大特征ACID
A:原子性：事务是最小的单位，不可以再分割
C:一致性：事务要求，同一个事务中的sql语句，必须保证同时成功或者同时失败
I:隔离性：事务1和事务2之间是有隔离性的
D:持久性：事务一旦结束（commit,rollback）,就不可以返回
事务开启：
1.修改默认提交 set autocommit=0;
2.begin;
3.start transaction;
事务手动提交：
commit;
事务手动回滚：
rollback;
事务的隔离性：
1.read uncommitted; 读未提交的
2.read committed; 读已经提交的
3.repeatable read; 可以重复读
4.serializable; 串行化
20.1脏读(read uncommitted)
脏读：一个事务读到了另一个事务没有提交的数据，就叫做脏读
1.read uncommitted;
如果有事务a和事务b，a事务对数据进行操作，在操作过程中，事务没有被提交，但是b可以看见a操作的结果。
bank数据库user表
insert into user values(3,'小明',1000);
insert into user values(4,'淘宝店',1000);
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
+----+-----------+-------+
4 rows in set (0.00 sec)
--如何查看数据库的隔离级别？
mysql 8.0
--系统级别
select @@global.transaction_isolation;
--会话级别
select @@transaction_isolation;
--mysql默认隔离级别（可重复读）
mysql> select @@global.transaction_isolation;
+--------------------------------+
| @@global.transaction_isolation |
+--------------------------------+
| REPEATABLE-READ |
+--------------------------------+
1 row in set (0.00 sec)
--修改隔离级别
set global transaction isolation level read uncommitted;
mysql> set global transaction isolation level read uncommitted;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@global.transaction_isolation;
+--------------------------------+
| @@global.transaction_isolation |
+--------------------------------+
| READ-UNCOMMITTED |
+--------------------------------+
1 row in set (0.00 sec)
--转账：小明在淘宝店买鞋子：800
小明-》城都 ATM
淘宝店-》广州 ATM
begin;
update user set money=money-800 where name='小明';
update user set money=money+800 where name='淘宝店';
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 200 |
| 4 | 淘宝店 | 1800 |
+----+-----------+-------+
4 rows in set (0.00 sec)
--给淘宝店打电话，说你去查一下，是不是到账了
--淘宝店重启一个终端
mysql> use bank;
Database changed
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 200 |
| 4 | 淘宝店 | 1800 |
+----+-----------+-------+
4 rows in set (0.00 sec)
--发货
--晚上请客吃饭花了1800
--小明突然rollback
mysql> rollback;
Query OK, 0 rows affected (0.03 sec)
--结账发现钱不够
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
+----+-----------+-------+
4 rows in set (0.00 sec)
--如果两个不同的地方，都在进行操作，如果事务a开启之后，他的数据可以被其他事务读取到
--这样就会出现（脏读）
--脏读：一个事务读到了另一个事务没有提交的数据，就叫做脏读
--实际开发中是不允许出现脏读的
20.2不可重复读（read committed）
–虽然我只能读到你提交的数据，但是还是会出现问题
–读取同一个表的数据，发现前后不一致
2.read committed; 读已经提交的
--修改隔离级别为 READ-COMMITTED
set global transaction isolation level read committed;
mysql> select @@global.transaction_isolation;
+--------------------------------+
| @@global.transaction_isolation |
+--------------------------------+
| READ-COMMITTED |
+--------------------------------+
1 row in set (0.00 sec)
--bank数据库user表
--小张：银行的会计
start transaction;
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
+----+-----------+-------+
4 rows in set (0.00 sec)
--小张出门了一下
--小王：
mysql> use bank;
Database changed
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into user values(5,'c',100);
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.08 sec)
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
+----+-----------+-------+
5 rows in set (0.00 sec)
--小张回来了
mysql> select avg(money) from user;
+------------+
| avg(money) |
+------------+
| 820.0000 |
+------------+
1 row in set (0.00 sec)
--money 的平均不是1000，变少了？
--虽然我只能读到你提交的数据，但是还是会出现问题
--读取同一个表的数据，发现前后不一致
--不可重复读：read committed;
20.3可重复读（repeatable read）
–事务a和事务b同时操作一张表，事务a提交的数据，也不能被事务b读到，就造成幻读。
set global transaction isolation level repeatable read;
mysql> select @@global.transaction_isolation;
+--------------------------------+
| @@global.transaction_isolation |
+--------------------------------+
| REPEATABLE-READ |
+--------------------------------+
1 row in set (0.00 sec)
--在 REPEATABLE-READ 隔离级别下会出现什么问题？
--张三--成都
start transaction;
--李四--北京
start transaction;
--张三--成都
mysql> insert into user values(6,'d',1000);
Query OK, 1 row affected (0.00 sec)
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
| 6 | d | 1000 |
+----+-----------+-------+
6 rows in set (0.00 sec)
--李四--北京
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
+----+-----------+-------+
5 rows in set (0.00 sec)
--张三--成都
mysql> commit;
Query OK, 0 rows affected (0.10 sec)
--李四--北京
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
+----+-----------+-------+
5 rows in set (0.00 sec)
mysql> insert into user values(6,'d',1000);
ERROR 1062 (23000): Duplicate entry '6' for key 'user.PRIMARY'
--这种现象就叫做幻读
--事务a和事务b同时操作一张表，事务a提交的数据，也不能被事务b读到，就造成幻读。
20.4串行化（serializable）
–当user被另外一个事务操作的时候，其他事务里面的写操作是不可以进行的
–进入排队状态，直到前面的事务结束之后，在没有等待超时的情况下现在的事务才可以执行写入操作
--修改隔离级别为串行化
set global transaction isolation level serializable;
mysql> select @@global.transaction_isolation;
+--------------------------------+
| @@global.transaction_isolation |
+--------------------------------+
| SERIALIZABLE |
+--------------------------------+
1 row in set (0.00 sec)
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
| 6 | d | 1000 |
+----+-----------+-------+
6 rows in set (0.00 sec)
--张三--成都
start transaction;
--李四--北京
start transaction;
--张三--成都
mysql> insert into user values(7,'赵铁柱',1000);
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.12 sec)
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
| 6 | d | 1000 |
| 7 | 赵铁柱 | 1000 |
+----+-----------+-------+
7 rows in set (0.00 sec)
--李四--北京
mysql> select * from user;
+----+-----------+-------+
| id | name | money |
+----+-----------+-------+
| 1 | tom | 900 |
| 2 | jack | 1100 |
| 3 | 小明 | 1000 |
| 4 | 淘宝店 | 1000 |
| 5 | c | 100 |
| 6 | d | 1000 |
| 7 | 赵铁柱 | 1000 |
+----+-----------+-------+
7 rows in set (0.00 sec)
--张三--成都
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into user values(8,'王小花',1000);
--等待状态，无法插入
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
--李四--北京
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
--张三--成都
mysql> insert into user values(8,'王小花',1000);
Query OK, 1 row affected (0.00 sec)
--此时插入成功
--当user被另外一个事务操作的时候，其他事务里面的写操作是不可以进行的
--进入排队状态，直到前面的事务结束之后，在没有等待超时的情况下现在的事务才可以执行写入操作
--串行化带来的问题：性能特差
20.5总结
总结：read uncommitted>read committed>repeatable read>serializable
--隔离级别越高，性能越差
mysql默认隔离级别是repeatable read