mysql 数据库 II（数据类型）

1.今日内容

1. 搜索引擎介绍
   • innodb
   • myisam
   • memory
2. mysql中的数据类型
   • 数据 int tinyint float
   • 时间 datetime date time
   • 字符串 char varchar
   • enum set

2.具体内容

1. 搜索引擎介绍

   • innodb

   1.事务（保证数字安全，数据的完整性）
   2.row-level locking。行级锁
   3.table-level locking。 表级锁
   4.foreign keys  外键锁
   5.加速查询（树型结构+表结构）
   
   
   MySql 5.6 版本默认的存储引擎。InnoDB 是一个事务安全的存储引擎，它具备提交、回滚以及崩溃恢复的功能以保护用户数据。InnoDB 的行级别锁定以及 Oracle 风格的一致性无锁读提升了它的多用户并发数以及性能。InnoDB 将用户数据存储在聚集索引中以减少基于主键的普通查询所带来的 I/O 开销。为了保证数据的完整性，InnoDB 还支持外键约束。
   

   • myisam

   1.table-level locking。 表级锁
   2.加速查询（树型结构+表结构）
   
   
   MyISAM既不支持事务、也不支持外键、其优势是访问速度快，但是表级别的锁定限制了它在读写负载方面的性能，因此它经常应用于只读或者以读为主的数据场景。
   

   • memory

   1.基于hash
   
   
   在内存中存储所有数据，应用于对非关键数据由快速查找的场景。Memory类型的表访问数据非常快，因为它的数据是存放在内存中的，并且默认使用HASH索引，但是一旦服务关闭，表中的数据就会丢失
   

2. mysql中的数据类型

   • 数据 int tinyint float

   int示例

   #int示例
   
   #创建一个表，一个默认宽度的int，一个指定宽度的int（5）
   mysql> create table t1(id1 int ,id2 int(5));
   Query OK, 0 rows affected (0.03 sec)
   
   #插入数据1
   mysql> insert into t1 values(1,1);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t1;
   +------+------+
   | id1  | id2  |
   +------+------+
   |    1 |    1 |
   +------+------+
   1 row in set (0.00 sec)
   
   mysql> insert into t1 values (111111,111111);
   Query OK, 1 row affected (0.00 sec)
   
   #id2显示了正确的数值，没有受到宽度限制的影响
   mysql> select * from t1;
   +--------+--------+
   | id1    | id2    |
   +--------+--------+
   |      1 |      1 |
   | 111111 | 111111 |
   +--------+--------+
   2 rows in set (0.00 sec)
   
   mysql> show create table t1;
   +-------+--------------------------------------------------------------------------------------------------------------------+
   | Table | Create Table                                                                                                       |
   +-------+--------------------------------------------------------------------------------------------------------------------+
   | t1    | CREATE TABLE `t1` (
     `id1` int(11) DEFAULT NULL,
     `id2` int(5) DEFAULT NULL
   ) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
   +-------+--------------------------------------------------------------------------------------------------------------------+
   1 row in set (0.00 sec)
   
   mysql> into t1 values (22222222,22222222);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t1;
   +----------+----------+
   | id1      | id2      |
   +----------+----------+
   |        1 |        1 |
   |   111111 |   111111 |
   | 22222222 | 22222222 |
   +----------+----------+
   3 rows in set (0.00 sec)
   
   #修改id1字段，给字段添加一个unsigned表示无符号
   mysql> alter table t1 modify id1 int unsigned;
   Query OK, 3 rows affected (0.04 sec)
   Records: 3  Duplicates: 0  Warnings: 0
   
   mysql> desc t1;
   +-------+------------------+------+-----+---------+-------+
   | Field | Type             | Null | Key | Default | Extra |
   +-------+------------------+------+-----+---------+-------+
   | id1   | int(10) unsigned | YES  |     | NULL    |       |
   | id2   | int(5)           | YES  |     | NULL    |       |
   +-------+------------------+------+-----+---------+-------+
   2 rows in set (0.00 sec)
   
   #当给id1添加的数据大于2147483647时，可以顺利插入
   mysql> insert into t1 values (2147483648,2147483647);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t1;
   +------------+------------+
   | id1        | id2        |
   +------------+------------+
   |          1 |          1 |
   |     111111 |     111111 |
   |   22222222 |   22222222 |
   | 2147483648 | 2147483647 |
   +------------+------------+
   4 rows in set (0.00 sec)
   
   #当个id2添加的数据大于2147483647时，会报错
   mysql> insert into t1 values (2147483648,2147483649);
   ERROR 1264 (22003): O
   

   小数示例

   #小数示例
   
   mysql> create table t2 (id1 float(5,2),id2 double(5,2),id3 decimal(5,2));
   Query OK, 0 rows affected (0.02 sec)
   
   mysql> desc t2;
   +-------+--------------+------+-----+---------+-------+
   | Field | Type         | Null | Key | Default | Extra |
   +-------+--------------+------+-----+---------+-------+
   | id1   | float(5,2)   | YES  |     | NULL    |       |
   | id2   | double(5,2)  | YES  |     | NULL    |       |
   | id3   | decimal(5,2) | YES  |     | NULL    |       |
   +-------+--------------+------+-----+---------+-------+
   3 rows in set (0.00 sec)
   
   mysql> insert into t2 values(1.23,1.23,1.23);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t2;
   +------+------+------+
   | id1  | id2  | id3  |
   +------+------+------+
   | 1.23 | 1.23 | 1.23 |
   +------+------+------+
   1 row in set (0.00 sec)
   
   mysql> insert into t2 values(1.234,1.234,1.234);
   Query OK, 1 row affected, 1 warning (0.01 sec)
   
   #向表中插入1.234，会发现4都被截断了
   mysql> select * from t2;
   +------+------+------+
   | id1  | id2  | id3  |
   +------+------+------+
   | 1.23 | 1.23 | 1.23 |
   | 1.23 | 1.23 | 1.23 |
   +------+------+------+
   2 rows in set (0.00 sec)
   
   mysql> insert into t2 values(1.235,1.235,1.235);
   Query OK, 1 row affected, 1 warning (0.00 sec)
   
   #遵循四舍五入的规则
   mysql> select * from t2;
   +------+------+------+
   | id1  | id2  | id3  |
   +------+------+------+
   | 1.23 | 1.23 | 1.23 |
   | 1.23 | 1.23 | 1.23 |
   | 1.24 | 1.24 | 1.24 |
   +------+------+------+
   3 rows in set (0.00 sec)
   
   #去掉参数约束
   mysql> create table t3(id1 float,id2 double,id3 decimal);
   Query OK, 0 rows affected (0.01 sec)
   
   mysql> insert into t3 values(1.234,1.234,1.234);
   Query OK, 1 row affected, 1 warning (0.00 sec)
   
   #发现decimal默认值是（10，0）的整数
   mysql> select * from t3;
   +-------+-------+------+
   | id1   | id2   | id3  |
   +-------+-------+------+
   | 1.234 | 1.234 |    1 |
   +-------+-------+------+
   1 row in set (0.00 sec)
   
   mysql> insert into t3 values(1.2345678,1.2345678678,1.2345678);
   Query OK, 1 row affected, 1 warning (0.00 sec)
   
   #当对小数位没有约束的时候，输入超长的小数，发现float和double的区别
   mysql> select * from t3;
   +---------+--------------+------+
   | id1     | id2          | id3  |
   +---------+--------------+------+
   |   1.234 |        1.234 |    1 |
   | 1.23457 | 1.2345678678 |    1 |
   +---------+--------------+------+
   2 rows in set (0.00 sec)
   
   

   • 时间 datetime date time

   date ，time，datetime示例

   mysql> create table t4(d date,t time,dt datetime);
   Query OK, 0 rows affected (0.02 sec)
   
   mysql> desc t4;
   +-------+----------+------+-----+---------+-------+
   | Field | Type     | Null | Key | Default | Extra |
   +-------+----------+------+-----+---------+-------+
   | d     | date     | YES  |     | NULL    |       |
   | t     | time     | YES  |     | NULL    |       |
   | dt    | datetime | YES  |     | NULL    |       |
   +-------+----------+------+-----+---------+-------+
   3 rows in set (0.00 sec)
   
   mysql> insert into t4 values(now(),now(),now());
   Query OK, 1 row affected, 1 warning (0.00 sec)
   
   mysql> select * from t4;
   +------------+----------+---------------------+
   | d          | t        | dt                  |
   +------------+----------+---------------------+
   | 2020-01-07 | 22:12:29 | 2020-01-07 22:12:29 |
   +------------+----------+---------------------+
   1 row in set (0.00 sec)
   
   mysql> insert into t4 values(null,null,null);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t4;
   +------------+----------+---------------------+
   | d          | t        | dt                  |
   +------------+----------+---------------------+
   | 2020-01-07 | 22:12:29 | 2020-01-07 22:12:29 |
   | NULL       | NULL     | NULL                |
   +------------+----------+---------------------+
   2 rows in set (0.00 sec)
   

   timestamp示例

   #timestamp示例
   
   mysql> create table t5 (id1 timestamp);
   Query OK, 0 rows affected (0.01 sec)
   
   mysql> desc t5;
   +-------+-----------+------+-----+-------------------+-----------------------------+
   | Field | Type      | Null | Key | Default           | Extra                       |
   +-------+-----------+------+-----+-------------------+-----------------------------+
   | id1   | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
   +-------+-----------+------+-----+-------------------+-----------------------------+
   1 row in set (0.00 sec)
   
   #插入数据null，会自动插入当前时间的时间
   mysql> insert  values(null);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t5;
   +---------------------+
   | id1                 |
   +---------------------+
   | 2020-01-07 22:15:26 |
   +---------------------+
   1 row in set (0.00 sec)
   
   mysql> alter table t5 add id2 timestamp;
   ERROR 1067 (42000): Invalid default value for 'id2'
   
   #设置默认时间为当前的时间
   mysql> alter table t5 add id2 timestamp default current_timestamp;
   Query OK, 0 rows affected (0.07 sec)
   Records: 0  Duplicates: 0  Warnings: 0
   
   mysql> select * from t5;
   +---------------------+---------------------+
   | id1                 | id2                 |
   +---------------------+---------------------+
   | 2020-01-07 22:15:26 | 2020-01-07 22:21:41 |
   +---------------------+---------------------+
   1 row in set (0.00 sec)
   
   mysql> show create table t5;
   +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Table | Create Table                                                                                                                                                                                    |
   +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | t5    | CREATE TABLE `t5` (
     `id1` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
     `id2` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
   ) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
   +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   1 row in set (0.00 sec)
   
   mysql> inser t5 values (null,null);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t5;
   +---------------------+---------------------+
   | id1                 | id2                 |
   +---------------------+---------------------+
   | 2020-01-07 22:15:26 | 2020-01-07 22:21:41 |
   | 2020-01-07 22:23:04 | 2020-01-07 22:23:04 |
   +---------------------+---------------------+
   2 rows in set (0.00 sec)
   
   
   mysql> insert into t5 values (19700101080001);
   ERROR 1136 (21S01): Column count doesn't match value count at row 1
     
   mysql> insert into t5 values (19700101080001,null);
   Query OK, 1 row affected (0.01 sec)
   
   mysql> select * from t5;
   +---------------------+---------------------+
   | id1                 | id2                 |
   +---------------------+---------------------+
   | 2020-01-07 22:15:26 | 2020-01-07 22:21:41 |
   | 2020-01-07 22:23:04 | 2020-01-07 22:23:04 |
   | 1970-01-01 08:00:01 | 2020-01-07 22:25:39 |
   +---------------------+---------------------+
   3 rows in set (0.00 sec)
   
   #timestamp时间下限是19700101080001
   mysql> insert into t5 values (19700101080000,null);
   ERROR 1292 (22007): Incorrect datetime value: '19700101080000' for column 'id1' at row 1
       
   mysql> insert into t5 values('2038-01-19 11:14:07',null);
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t5;
   +---------------------+---------------------+
   | id1                 | id2                 |
   +---------------------+---------------------+
   | 2020-01-07 22:15:26 | 2020-01-07 22:21:41 |
   | 2020-01-07 22:23:04 | 2020-01-07 22:23:04 |
   | 1970-01-01 08:00:01 | 2020-01-07 22:25:39 |
   | 2038-01-19 11:14:07 | 2020-01-07 22:27:09 |
   +---------------------+---------------------+
   4 rows in set (0.00 sec)
   
   #timestamp时间的上限是2038-01-19 11：14：07
   mysql> insert into t5 values('2038-01-19 11:14:08',null);
   ERROR 1292 (22007): Incorrect datetime value: '2038-01-19 11:14:08' for column 'id1' at row 1
   

   datetime示例

   #datetime示例
   
   mysql> create table t6 (dt datetime);
   Query OK, 0 rows affected (0.01 sec)
   
   mysql> desc t6;
   +-------+----------+------+-----+---------+-------+
   | Field | Type     | Null | Key | Default | Extra |
   +-------+----------+------+-----+---------+-------+
   | dt    | datetime | YES  |     | NULL    |       |
   +-------+----------+------+-----+---------+-------+
   1 row in set (0.00 sec)
   
   mysql> insert into t6 values('2019-9-2 12:20:11');
   Query OK, 1 row affected (0.00 sec)
   
   mysql> insert into t6 values('2018/9/2 12:20:11');
   Query OK, 1 row affected (0.01 sec)
   
   mysql> insert into t6 values ('20180902122011');
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t6;
   +---------------------+
   | dt                  |
   +---------------------+
   | 2019-09-02 12:20:11 |
   | 2018-09-02 12:20:11 |
   | 2018-09-02 12:20:11 |
   +---------------------+
   3 rows in set (0.00 sec)
   

   • 字符串 char varchar

   char varchar示例

   mysql> create table t7 (v varchar(4),c char(4));
   Query OK, 0 rows affected (0.01 sec)
   
   mysql> desc t7;
   +-------+------------+------+-----+---------+-------+
   | Field | Type       | Null | Key | Default | Extra |
   +-------+------------+------+-----+---------+-------+
   | v     | varchar(4) | YES  |     | NULL    |       |
   | c     | char(4)    | YES  |     | NULL    |       |
   +-------+------------+------+-----+---------+-------+
   2 rows in set (0.00 sec)
   
   mysql> insert into t7 values ('ab  ','ab  ');
   Query OK, 1 row affected (0.00 sec)
   
   #在检索的时候char数据类型会去掉空格
   mysql> select * from t7 ;
   +------+------+
   | v    | c    |
   +------+------+
   | ab   | ab   |
   +------+------+
   1 row in set (0.00 sec)
   
   #查询结果计算的长度
   mysql> select length(v),length(c) from t7;
   +-----------+-----------+
   | length(v) | length(c) |
   +-----------+-----------+
   |         4 |         2 |
   +-----------+-----------+
   1 row in set (0.02 sec)
   
   #给结构拼上一个加号
   mysql> select concat(v,'+'),concat(c,'+') from t7;
   +---------------+---------------+
   | concat(v,'+') | concat(c,'+') |
   +---------------+---------------+
   | ab  +         | ab+           |
   +---------------+---------------+
   1 row in set (0.00 sec)
   
   #当存储的长度超出定义的长度，会截断
   mysql> insert into t7 values ('abcd   ','abcd   ');
   Query OK, 1 row affected, 1 warning (0.00 sec)
   
   mysql> select concat(v,'+'),concat(c,'+') from t7;
   +---------------+---------------+
   | concat(v,'+') | concat(c,'+') |
   +---------------+---------------+
   | ab  +         | ab+           |
   | abcd+         | abcd+         |
   +---------------+---------------+
   2 rows in set (0.00 sec)
   

   • enum set

   enum set示例

   mysql> create table t8(name char(20),gender enum('female','male'));
   Query OK, 0 rows affected (0.02 sec)
   
   mysql> desc t8;
   +--------+-----------------------+------+-----+---------+-------+
   | Field  | Type                  | Null | Key | Default | Extra |
   +--------+-----------------------+------+-----+---------+-------+
   | name   | char(20)              | YES  |     | NULL    |       |
   | gender | enum('female','male') | YES  |     | NULL    |       |
   +--------+-----------------------+------+-----+---------+-------+
   2 rows in set (0.00 sec)
   
   # 选择enum('female','male')中的一项作为gender的值，可以正常插入
   mysql> insert into t8 values ('chen','male');
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t8;
   +------+--------+
   | name | gender |
   +------+--------+
   | chen | male   |
   +------+--------+
   1 row in set (0.00 sec)
   
   # 不能同时插入('female','male')两个值，也不能插入不属于('female','male')的值
   mysql> insert into t8 values ('chen','male,female');
   ERROR 1265 (01000): Data truncated for column 'gender' at row 1
   mysql> create table t9 (name char(20),hobby set('看书','打乒乓球','玩游戏','旅游'));
   Query OK, 0 rows affected (0.02 sec)
   
   mysql> desc t9;
   +-------+---------------------------------------------------+------+-----+---------+-------+
   | Field | Type                                              | Null | Key | Default | Extra |
   +-------+---------------------------------------------------+------+-----+---------+-------+
   | name  | char(20)                                          | YES  |     | NULL    |       |
   | hobby | set('看书','打乒乓球','玩游戏','旅游')            | YES  |     | NULL    |       |
   +-------+---------------------------------------------------+------+-----+---------+-------+
   2 rows in set (0.01 sec)
   
   # 可以任意选择set('看书','打乒乓球','玩游戏','旅游')中的项，并带去重功能
   mysql> insert into t9 values ('chen','看书,玩游戏')；
       -> ;
   ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '；' at line 1
   mysql> insert into t9 values ('chen','看书,玩游戏');
   Query OK, 1 row affected (0.01 sec)
   
   mysql> select * from t9;
   +------+------------------+
   | name | hobby            |
   +------+------------------+
   | chen | 看书,玩游戏      |
   +------+------------------+
   1 row in set (0.00 sec)
   mysql> insert into t9 values ('chen','看书,看书,看书,旅游');
   Query OK, 1 row affected (0.00 sec)
   
   mysql> select * from t9;
   +------+------------------+
   | name | hobby            |
   +------+------------------+
   | chen | 看书,玩游戏      |
   | chen | 看书,旅游        |
   +------+------------------+
   2 rows in set (0.00 sec)
   
   # 不能选择不属于set('看书','打乒乓球','玩游戏','旅游')中的项
   mysql> insert into t9 values('chen','打游戏,听歌');
   ERROR 1265 (01000): Data truncated for column 'hobby' at row 1