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数据库基础二

存储引擎

InnoDB 支持事务，外键，行级锁
事务：一个最小的不可再分的工作单元；通常一个事务对应一个完整的业务

事务四大特性：

1.原子性(A)：事务是最小单位，不可再分
2.一致性(C)：事务要求所有的DML语句操作的时候，   必须保证同时成功或者同时失败
3.隔离性(I)：事务A和事务B之间具有隔离性
4.持久性(D)：是事务的保证，事务终结的标志(内存的数据持久到硬盘文件中)

关于事务的一些术语

开启事务：Start Transaction
事务结束：End Transaction
提交事务：Commit Transaction
回滚事务：Rollback Transaction

MyIsam 表级锁，支持全文索引
只查询多，修改少的时候使用
myisam，同一张表中的数据不能被同时修改
memory 每个用户的登录状态
数据都存在内存中，读取速度快
数据量小并对服务器的内存有要求
断电消失
blackhole 黑洞
放进去的所有数据都不存

sql语句

创建表

mysql> create table staff_info (id int,
       name varchar(20),
       age int,
       sex enum('female','male'),
       phone char(11),
       job varchar(20));
Query OK, 0 rows affected (0.20 sec)

查看表结构
mysql> desc staff_info;

+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(20)           | YES  |     | NULL    |       |
| age   | int(11)               | YES  |     | NULL    |       |
| sex   | enum('female','male') | YES  |     | NULL    |       |
| phone | char(11)              | YES  |     | NULL    |       |
| job   | varchar(20)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+

插入数据

指定列名插入数据
mysql> insert into staff_info (id,name,age,sex,phone,job) values (1,'aa',83,'female','13651054608','IT');
Query OK, 1 row affected (0.02 sec)

插入单行数据
mysql> insert into staff_info values (2,'xm',82,'female','13651054608','IT');
Query OK, 1 row affected (0.02 sec)

插入多行数据
 mysql> insert into staff_info values
     -> (2,'ww',26,'male','13304320533','Tearcher'),
     -> (3,'ls',25,'male','13332353222','IT'),
     -> (4,'zs',40,'male','13332353333','IT');

查询数据

# 查看所有列的数据
# mysql> select * from staff_info;
# +------+----------+------+--------+-------------+----------+
# | id   | name     | age  | sex    | phone       | job      |
# +------+----------+------+--------+-------------+----------+
# |    1 | xm     |   82 | female | 13651054608 | IT       |
# |    2 | ww     |   26 | male   | 13304320533 | Tearcher |
# |    3 | ls     |   25 | male   | 13332353222 | IT       |
# |    4 | zs     |   40 | male   | 13332353333 | IT       |
# +------+----------+------+--------+-------------+----------+

查看指定列的数据

# mysql> select name,age from staff_info;
# +----------+------+
# | name     | age  |
# +----------+------+
# | xm     |   82 |
# | ww     |   26 |
# | ls    |   25 |
# | zs |   40 |
# +----------+------+
# 4 rows in set (0.00 sec)

数据类型

常用
int
float
decimal

整数部分

# mysql> create table t5 (id1 int(4),id2 int);
# Query OK, 0 rows affected (0.16 sec)
#
# mysql> desc t5;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id1   | int(4)  | YES  |     | NULL    |       |
# | id2   | int(11) | YES  |     | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)
#
# mysql> insert into t5 values (123,123);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t5;
# +------+------+
# | id1  | id2  |
# +------+------+
# |  123 |  123 |
# +------+------+
# 1 row in set (0.00 sec)

# mysql> insert into t5 values (12345,12345);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t5;
# +-------+-------+
# | id1   | id2   |
# +-------+-------+
# |   123 |   123 |
# | 12345 | 12345 |
# +-------+-------+
# 2 rows in set (0.00 sec)
#
# mysql> insert into t5 values (123,2147483648);
# Query OK, 1 row affected, 1 warning (0.02 sec)
#
# mysql> select * from t5;
# +-------+------------+
# | id1   | id2        |
# +-------+------------+
# |   123 |        123 |
# | 12345 |      12345 |
# |   123 | 2147483647 |
# +-------+------------+
# 3 rows in set (0.00 sec)

# 范围测试 有符号和无符号
# mysql> create table t6 (id1 int(4),id2 int unsigned);
# Query OK, 0 rows affected (0.25 sec)
#
# mysql> insert into t6 values (123,2147483648);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t6;
# +------+------------+
# | id1  | id2        |
# +------+------------+
# |  123 | 2147483648 |
# +------+------------+
# 1 row in set (0.00 sec)

小数

# 长度约束测试
# mysql> create table t7 (f float(10,3),d double(10,3),d2 decimal(10,3));
# Query OK, 0 rows affected (0.20 sec)
#
# mysql> insert into t7 values (1.23456789,2.34567,3.56789);
# Query OK, 1 row affected, 1 warning (0.02 sec)
#
# mysql> select * from t7;
# +-------+-------+-------+
# | f     | d     | d2    |
# +-------+-------+-------+
# | 1.235 | 2.346 | 3.568 |
# +-------+-------+-------+
# 1 row in set (0.00 sec)

精度测试

# mysql> create table t8 (f float(255,30),d double(255,30),d2 decimal(65,30));
# Query OK, 0 rows affected (0.18 sec)
# mysql> insert into t8 values (1.11111111111111111111111111111111111111111111111111111111111,1.11111111111111111111111111111111111111111111111111111111111,1.11111111111111111111111111111111111111111111111111111111111);
# Query OK, 1 row affected, 1 warning (0.02 sec)
# mysql> select * from t8;
# +----------------------------------+----------------------------------+----------------------------------+
# | f                                | d                                | d2                               |
# +----------------------------------+----------------------------------+----------------------------------+
# | 1.111111164093017600000000000000 | 1.111111111111111200000000000000 | 1.111111111111111111111111111111 |
# +----------------------------------+----------------------------------+----------------------------------+

时间类型

常用
date      描述年月日
datetime  描述年月日时分秒

timestamp字段默认不为空

# mysql> create table t9 (d date,t time,y year,dt datetime,ts timestamp);
# Query OK, 0 rows affected (0.18 sec)
#
# mysql> desc t9;
# +-------+-----------+------+-----+-------------------+-----------------------------+
# | Field | Type      | Null | Key | Default           | Extra                       |
# +-------+-----------+------+-----+-------------------+-----------------------------+
# | d     | date      | YES  |     | NULL              |                             |
# | t     | time      | YES  |     | NULL              |                             |
# | y     | year(4)   | YES  |     | NULL              |                             |
# | dt    | datetime  | YES  |     | NULL              |                             |
# | ts    | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
# +-------+-----------+------+-----+-------------------+-----------------------------+
# 5 rows in set (0.01 sec)
#
# mysql> insert into t9 values (null,null,null,null,null);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t9;
# +------+------+------+------+---------------------+
# | d    | t    | y    | dt   | ts                  |
# +------+------+------+------+---------------------+
# | NULL | NULL | NULL | NULL | 2018-09-29 11:27:29 |
# +------+------+------+------+---------------------+
# 1 row in set (0.00 sec)
#
# mysql> insert into t9 values(now(),now(),now(),now(),now());
# Query OK, 1 row affected, 1 warning (0.03 sec)

每种数据类型表示的时间格式

# mysql> select * from t9;
# +------------+----------+------+---------------------+---------------------+
# | d          | t        | y    | dt                  | ts                  |
# +------------+----------+------+---------------------+---------------------+
# | NULL       | NULL     | NULL | NULL                | 2018-09-29 11:27:29 |
# | 2018-09-29 | 11:29:07 | 2018 | 2018-09-29 11:29:07 | 2018-09-29 11:29:07 |
# +------------+----------+------+---------------------+---------------------+
# 2 rows in set (0.00 sec)
#

datetime 和 timestamp的范围控制

# mysql> insert into t9 (dt) values (10010101000000);
# Query OK, 1 row affected (0.03 sec)

# mysql> select * from t9;
# +------------+----------+------+---------------------+---------------------+
# | d          | t        | y    | dt                  | ts                  |
# +------------+----------+------+---------------------+---------------------+
# | NULL       | NULL     | NULL | NULL                | 2018-09-29 11:27:29 |
# | 2018-09-29 | 11:29:07 | 2018 | 2018-09-29 11:29:07 | 2018-09-29 11:29:07 |
# | NULL       | NULL     | NULL | 1001-01-01 00:00:00 | 2018-09-29 11:30:33 |
# +------------+----------+------+---------------------+---------------------+
# 3 rows in set (0.00 sec)

# mysql>
# mysql> insert into t9 (ts) values (10010101000000);
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t9;
# +------------+----------+------+---------------------+---------------------+
# | d          | t        | y    | dt                  | ts                  |
# +------------+----------+------+---------------------+---------------------+
# | NULL       | NULL     | NULL | NULL                | 2018-09-29 11:27:29 |
# | 2018-09-29 | 11:29:07 | 2018 | 2018-09-29 11:29:07 | 2018-09-29 11:29:07 |
# | NULL       | NULL     | NULL | 1001-01-01 00:00:00 | 2018-09-29 11:30:33 |
# | NULL       | NULL     | NULL | NULL                | 0000-00-00 00:00:00 |
# +------------+----------+------+---------------------+---------------------+
# 4 rows in set (0.00 sec)

字符串类型

CHAR	0-255字节	定长字符串
    # 定长 浪费磁盘 存取速度非常快
VARCHAR	0-65535 字节	变长字符串
    # 变长 节省磁盘空间 存取速度相对慢

char(5)     '  abc'  5   'abcde'  5
    # 这一列数据的长度变化小  手机号 身份证号 学号
    # 频繁存取、对效率要求高
    # 短数据
varchar(5)  '3abc'   4   '5abcde' 6
    # 这一列的数据长度变化大  name  描述信息
    # 对效率要求相对小
    # 相对长

# mysql> create table t10 (c char(5),vc varchar(5));
# Query OK, 0 rows affected (0.14 sec)
#
# mysql> desc t10;
# +-------+------------+------+-----+---------+-------+
# | Field | Type       | Null | Key | Default | Extra |
# +-------+------------+------+-----+---------+-------+
# | c     | char(5)    | YES  |     | NULL    |       |
# | vc    | varchar(5) | YES  |     | NULL    |       |
# +-------+------------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)

# 插入ab，实际上存储中c占用5个字节，vc只占用3个字节，但是我们查询的额时候感知不到
# 因为char类型在查询的时候会默认去掉所有补全的空格
# mysql> insert into t10 values ('ab','ab');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t10;
# +------+------+
# | c    | vc   |
# +------+------+
# | ab   | ab   |
# +------+------+
# 1 row in set (0.00 sec)

# 插入的数据超过了约束的范围，会截断数据
# mysql> insert into t10 values ('abcdef','abcdef');
# Query OK, 1 row affected, 2 warnings (0.02 sec)
#
# mysql> select * from t10;
# +-------+-------+
# | c     | vc    |
# +-------+-------+
# | ab    | ab    |
# | abcde | abcde |
# +-------+-------+
# 2 rows in set (0.00 sec)

# 插入带有空格的数据，查询的时候能看到varchar字段是带空格显示的，char字段仍然在显示的时候去掉了空格
# mysql> insert into t10 values ('ab    ','ab    ');
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t10;
# +-------+-------+
# | c     | vc    |
# +-------+-------+
# | ab    | ab    |
# | abcde | abcde |
# | ab    | ab    |
# +-------+-------+
# 3 rows in set (0.00 sec)
#
# mysql> select concat(c,'+'),concat(vc,'+') from t10;
# +---------------+----------------+
# | concat(c,'+') | concat(vc,'+') |
# +---------------+----------------+
# | ab+           | ab+            |
# | abcde+        | abcde+         |
# | ab+           | ab   +         |
# +---------------+----------------+
# 3 rows in set (0.01 sec)

枚举和集合类型

枚举 enum   单选
集合 set    多选

# mysql> create table t11 (name varchar(20),sex enum('male','female'),hobby set('抽烟','喝酒','烫头','翻车'));
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t11;
# +-------+------------------------------------------+------+-----+---------+-------+
# | Field | Type                                     | Null | Key | Default | Extra |
# +-------+------------------------------------------+------+-----+---------+-------+
# | name  | varchar(20)                              | YES  |     | NULL    |       |
# | sex   | enum('male','female')                    | YES  |     | NULL    |       |
# | hobby | set('抽烟','喝酒','烫头','翻车')         | YES  |     | NULL    |       |
# +-------+------------------------------------------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)

# 如果插入的数据不在枚举或者集合范围内，数据无法插入表
# mysql> insert into t11 values ('alex','aaaa','bbbb');
# Query OK, 1 row affected, 2 warnings (0.02 sec)
#
# mysql> select * from t11;
# +------+------+-------+
# | name | sex  | hobby |
# +------+------+-------+
# | alex |      |       |
# +------+------+-------+
# 1 row in set (0.00 sec)

# 向集合中插入数据，自动去重
# mysql> insert into t11 values ('alex','female','抽烟,抽烟,烫头');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t11;
# +------+--------+---------------+
# | name | sex    | hobby         |
# +------+--------+---------------+
# | alex |        |               |
# | alex | female | 抽烟,烫头     |
# +------+--------+---------------+
# 2 rows in set (0.00 sec)

# 向集合中插入多条数据，不存在的项无法插入
# mysql> insert into t11 values ('alex','female','抽烟,抽烟,烫头,打豆豆');
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t11;
# +------+--------+---------------+
# | name | sex    | hobby         |
# +------+--------+---------------+
# | alex |        |               |
# | alex | female | 抽烟,烫头     |
# | alex | female | 抽烟,烫头     |
# +------+--------+---------------+
# 3 rows in set (0.00 sec)

完整性约束

not null      非空
unique        唯一 : 唯一可以有一个空
唯一 + 非空
primary key   主键  唯一+非空 加速查询 每张表只能有一个主键
foreign key   外键  Innodb

# primary key
    # 唯一+非空 每张表只能有一个主键
# not null      非空
# unique        唯一 : 唯一可以有一个空

# not null + 唯一
    # 有一个可以为空了

# mysql> create table t12 (id int primary key,name varchar(20) not null,phone char(11) not null unique);
# Query OK, 0 rows affected (0.20 sec)
#
# mysql> desc t12;
# +-------+-------------+------+-----+---------+-------+
# | Field | Type        | Null | Key | Default | Extra |
# +-------+-------------+------+-----+---------+-------+
# | id    | int(11)     | NO   | PRI | NULL    |       |
# | name  | varchar(20) | NO   |     | NULL    |       |
# | phone | char(11)    | NO   | UNI | NULL    |       |
# +-------+-------------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t12 (id,name) values (1,'alex');
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t12;
# +----+------+-------+
# | id | name | phone |
# +----+------+-------+
# |  1 | alex |       |
# +----+------+-------+
# 1 row in set (0.00 sec)
#
# mysql> insert into t12 (id,name) values (2,'egon');
# ERROR 1062 (23000): Duplicate entry '' for key 'phone'
# mysql> insert into t12 (id,name,phone) values (2,'egon','13434345678');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t12;
# +----+------+-------------+
# | id | name | phone       |
# +----+------+-------------+
# |  1 | alex |             |
# |  2 | egon | 13434345678 |
# +----+------+-------------+
# 2 rows in set (0.00 sec)

# 不能输入重复的值
# mysql> insert into t12 (name,phone) values ('egon','13434345678');
# ERROR 1062 (23000): Duplicate entry '13434345678' for key 'phone'
# mysql> insert into t12 (name,phone) values ('egon','13434345679');
# Query OK, 1 row affected, 1 warning (0.02 sec)

# mysql> select * from t12;
# +----+------+-------------+
# | id | name | phone       |
# +----+------+-------------+
# |  0 | egon | 13434345679 |
# |  1 | alex |             |
# |  2 | egon | 13434345678 |
# +----+------+-------------+
# 3 rows in set (0.00 sec)

# 主键也不能重复
# mysql> insert into t12 (name,phone) values ('egon','13434345677');
# ERROR 1062 (23000): Duplicate entry '0' for key 'PRIMARY'

# 创建部门表
# mysql> create table department (id int primary key auto_increment,dep_name varchar(20) not null);
# Query OK, 0 rows affected (0.16 sec)

# 创建员工表 外键关联部门表中的id字段
# mysql> create table staff (sid int primary key auto_increment,sname varchar(20) not null,dep_id int, foreign key(dep_id) references department(id));
# Query OK, 0 rows affected (0.21 sec)

# mysql> desc staff;
# +--------+-------------+------+-----+---------+----------------+
# | Field  | Type        | Null | Key | Default | Extra          |
# +--------+-------------+------+-----+---------+----------------+
# | sid    | int(11)     | NO   | PRI | NULL    | auto_increment |
# | sname  | varchar(20) | NO   |     | NULL    |                |
# | dep_id | int(11)     | YES  | MUL | NULL    |                |
# +--------+-------------+------+-----+---------+----------------+
# 3 rows in set (0.01 sec)
#
# mysql> show create table staff;
# | Table | 
Create Table staff CREATE TABLE `staff` (
#   `sid` int(11) NOT NULL AUTO_INCREMENT,
#   `sname` varchar(20) NOT NULL,
#   `dep_id` int(11) DEFAULT NULL,
#   PRIMARY KEY (`sid`),
#   KEY `dep_id` (`dep_id`),
#   CONSTRAINT `staff_ibfk_1` FOREIGN KEY (`dep_id`) REFERENCES `department` (`id`)
# ) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
# 1 row in set (0.00 sec)

完整性约束补充

not null      非空
    # default 默认值
        # 如果不输入就是用默认的实质
unique        唯一 : 唯一可以有一个空
    # auto_increment  只有数字类型才能设置自增
    # 联合唯一
        # 就是给一个以上的字段设置 唯一约束
primary key   主键  唯一+非空 加速查询 每张表只能有一个主键
    # 当我们以非空并且唯一的约束来创建一个表的时候，
    # 如果我们没有指定主键，那么第一个非空唯一的字段将会被设置成主键
    # 联合主键
        # 就是给一个以上的字段设置 唯一非空约束

foreign key   外键  Innodb
    # 外表中的一个唯一字段
    # on delete cascade
    # on update cascade

# course : cid,cname,cprice
# student : sid,sname,age,course_id

# 如果我们没有指定主键，那么第一个非空唯一的字段将会被设置成主键
# mysql> create table t13 (id int unique not null);
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t13;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id    | int(11) | NO   | PRI | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 1 row in set (0.01 sec)
#
# # 非空 + 唯一约束不能插入空值
# mysql> insert into t13 values (null);
# ERROR 1048 (23000): Column 'id' cannot be null
# mysql> create table t14 (id1 int unique not null,id2 int unique not null);
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> desc t14;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id1   | int(11) | NO   | PRI | NULL    |       |
# | id2   | int(11) | NO   | UNI | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)

# # 主键不能为空值
# mysql> insert into t14 (id1) values (1);
# ERROR 1364 (HY000): Field 'id2' doesn't have a default value

# 指定主键之后 其他的非空 + 唯一约束都不会再成为主键
# mysql> create table t15 (id1 int unique not null,id2 int primary key);
# Query OK, 0 rows affected (0.23 sec)
#
# mysql> desc t15;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id1   | int(11) | NO   | UNI | NULL    |       |
# | id2   | int(11) | NO   | PRI | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)
#
# mysql> insert into t15 values (1,2);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t15 values (2,3);
# Query OK, 1 row affected (0.02 sec)
#
# mysql> insert into t15 values (4,4);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t15 values (4,5);
# ERROR 1062 (23000): Duplicate entry '4' for key 'id1'
# mysql>

# 设置联合主键
# mysql> create table t16 (id int,ip char(15),port int ,primary key(ip,port));
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t16;
# +-------+----------+------+-----+---------+-------+
# | Field | Type     | Null | Key | Default | Extra |
# +-------+----------+------+-----+---------+-------+
# | id    | int(11)  | YES  |     | NULL    |       |
# | ip    | char(15) | NO   | PRI |         |       |
# | port  | int(11)  | NO   | PRI | 0       |       |
# +-------+----------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t16 values (1,'192.168.0.1','9000');
# Query OK, 1 row affected (0.02 sec)
#
# mysql> insert into t16 values (1,'192.168.0.1','9001');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t16 values (1,'192.168.0.2','9000');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t16
#     -> ;
# +------+-------------+------+
# | id   | ip          | port |
# +------+-------------+------+
# |    1 | 192.168.0.1 | 9000 |
# |    1 | 192.168.0.1 | 9001 |
# |    1 | 192.168.0.2 | 9000 |
# +------+-------------+------+
# 3 rows in set (0.00 sec)
#
# mysql> insert into t16 values (2,'192.168.0.2','9000');
# ERROR 1062 (23000): Duplicate entry '192.168.0.2-9000' for key 'PRIMARY'
# mysql>

# 设置ip和port两个字段联合唯一
# mysql> create table t17 (id int primary key,ip char(15) not null ,port int not null, unique(ip,port));
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> desc t17;
# +-------+----------+------+-----+---------+-------+
# | Field | Type     | Null | Key | Default | Extra |
# +-------+----------+------+-----+---------+-------+
# | id    | int(11)  | NO   | PRI | NULL    |       |
# | ip    | char(15) | NO   | MUL | NULL    |       |
# | port  | int(11)  | NO   |     | NULL    |       |
# +-------+----------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t17 values (1,'192.168.0.1',9000);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t17 values (2,'192.168.0.1',9000);
# ERROR 1062 (23000): Duplicate entry '192.168.0.1-9000' for key 'ip'
# mysql> insert into t17 values (2,'192.168.0.1',9001);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t17 values (3,'192.168.0.2',9001);
# Query OK, 1 row affected (0.03 sec)

# default 设置默认值
# mysql> create table t18 (id int primary key auto_increment,name varchar(20) not null,sex enum('male','female')
#     -> not null default 'male');
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t18;
# +-------+-----------------------+------+-----+---------+----------------+
# | Field | Type                  | Null | Key | Default | Extra          |
# +-------+-----------------------+------+-----+---------+----------------+
# | id    | int(11)               | NO   | PRI | NULL    | auto_increment |
# | name  | varchar(20)           | NO   |     | NULL    |                |
# | sex   | enum('male','female') | NO   |     | male    |                |
# +-------+-----------------------+------+-----+---------+----------------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t18 (name) values ('alex');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t18;
# +----+------+------+
# | id | name | sex  |
# +----+------+------+
# |  1 | alex | male |
# +----+------+------+
# 1 row in set (0.00 sec)
#
# mysql> insert into t18 (name) values ('egon'),('yuan'),('nazha');
# Query OK, 3 rows affected (0.02 sec)
# Records: 3  Duplicates: 0  Warnings: 0
#
# mysql> select * from t18;
# +----+-------+------+
# | id | name  | sex  |
# +----+-------+------+
# |  1 | alex  | male |
# |  2 | egon  | male |
# |  3 | yuan  | male |
# |  4 | nazha | male |
# +----+-------+------+
# 4 rows in set (0.00 sec)
#
# mysql> insert into t18 (name,sex) values ('yanglan','female');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t18;
# +----+---------+--------+
# | id | name    | sex    |
# +----+---------+--------+
# |  1 | alex    | male   |
# |  2 | egon    | male   |
# |  3 | yuan    | male   |
# |  4 | nazha   | male   |
# |  5 | yanglan | female |
# +----+---------+--------+
# 5 rows in set (0.00 sec)

# 外键 只有另一个表中设置了unique的字段才能作为本表的外键
# mysql> create table t20 (id int,age int,t19_id int,foreign key(t19_id) references t19(id));
# ERROR 1215 (HY000): Cannot add foreign key constraint
# mysql> create table t21 (id int unique ,name varchar(20));
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> create table t20 (id int,age int,t_id int,foreign key(t_id) references t21(id));
# Query OK, 0 rows affected (0.21 sec)
#
# mysql> insert into t21 values (1,'python'),(2,'linux');
# Query OK, 2 rows affected (0.02 sec)

# 如果一个表找中的字段作为外键对另一个表提供服务，那么默认不能直接删除外表中正在使用的数据
# mysql> insert into t20 values (1,18,1);
# Query OK, 1 row affected (0.02 sec)
#
# mysql> insert into t20 values (2,38,2);
# Query OK, 1 row affected (0.02 sec)
#
# mysql> select * from t21;
# +------+--------+
# | id   | name   |
# +------+--------+
# |    1 | python |
# |    2 | linux  |
# +------+--------+
# 2 rows in set (0.00 sec)
#
# mysql> delete from t21 where id=1;
# ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`db2`.`t20`, CONSTRAINT `t20_ibfk_1` FOREIGN KEY (`t_id`) REFERENCES `t21` (`id`))

# 外键 on delete cascade on update cascade
# mysql> create table course (cid int primary key auto_increment,cname varchar(20) not null,
#     -> cprice int not null);
# Query OK, 0 rows affected (0.16 sec)
#
# mysql> create table student (sid int primary key auto_increment,
#     -> sname varchar(20) not null,
#     -> age int not null,
#     -> course_id int,
#     -> foreign key(course_id)
#     -> references course(cid)
#     -> on delete cascade
#     -> on update cascade);
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> insert into course (cname,cprice) values ('python',19800),('linux',15800);
# Query OK, 2 rows affected (0.03 sec)
# Records: 2  Duplicates: 0  Warnings: 0
#
# mysql> insert into student (sname,age,course_id) values ('yangzonghe',18,1),('hesihao',88,2);
# Query OK, 2 rows affected (0.03 sec)
# Records: 2  Duplicates: 0  Warnings: 0
#
# mysql> delete from course where cid = 1;
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from student;
# +-----+---------+-----+-----------+
# | sid | sname   | age | course_id |
# +-----+---------+-----+-----------+
# |   2 | hesihao |  88 |         2 |
# +-----+---------+-----+-----------+
# 1 row in set (0.00 sec)
#
# mysql> update course set cid = 1 where cid = 2;
# Query OK, 1 row affected (0.03 sec)
# Rows matched: 1  Changed: 1  Warnings: 0
#
# mysql> select * from course;
# +-----+-------+--------+
# | cid | cname | cprice |
# +-----+-------+--------+
# |   1 | linux |  15800 |
# +-----+-------+--------+
# 1 row in set (0.00 sec)
#
# mysql> select * from student;
# +-----+---------+-----+-----------+
# | sid | sname   | age | course_id |
# +-----+---------+-----+-----------+
# |   2 | hesihao |  88 |         1 |
# +-----+---------+-----+-----------+
# 1 row in set (0.00 sec)

表结构的修改

语法：
1. 修改表名
      ALTER TABLE 表名 
                      RENAME 新表名;

2. 增加字段
      ALTER TABLE 表名
                      ADD 字段名  数据类型 [完整性约束条件…],
                      ADD 字段名  数据类型 [完整性约束条件…];
                            
3. 删除字段
      ALTER TABLE 表名 
                      DROP 字段名;

4. 修改字段
      ALTER TABLE 表名 
                      MODIFY  字段名 数据类型 [完整性约束条件…];
      ALTER TABLE 表名 
                      CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…];
      ALTER TABLE 表名 
                      CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];

5.修改字段排列顺序/在增加的时候指定字段位置
    ALTER TABLE 表名
                     ADD 字段名  数据类型 [完整性约束条件…]  FIRST;
    ALTER TABLE 表名
                     ADD 字段名  数据类型 [完整性约束条件…]  AFTER 字段名;
    ALTER TABLE 表名
                     CHANGE 字段名  旧字段名 新字段名 新数据类型 [完整性约束条件…]  FIRST;
    ALTER TABLE 表名
                     MODIFY 字段名  数据类型 [完整性约束条件…]  AFTER 字段名;

查看全文

相关阅读:
多表查询
 合并查询与连接查询区别
 union 合并查询语法
 外连接查询left join on 左连接 right join on 右连接
 inner join on 三表查询四表查询5表查询不管多少表都可以
 INEER JOIN..ON两表查询例子
 sql server 三表查询
 两表查询语句
 内连接查询
 转：Exchange Server 2013 一步步安装图解

原文地址：https://www.cnblogs.com/echo-up/p/9726638.html