MySQL 数据库基础 二

一. 操作表

创建表

语法：

​ create table 表名(
​ 字段名 列类型 [可选的参数], ### 记住加逗号
​ 字段名 列类型 [可选的参数], ### 记住加逗号
​ 字段名 列类型 [可选的参数] ### 最后一行不加逗号
​ .....
​ )charset=utf8; #### 后面加分号

列约束：（******）

    auto_increment :  自增 1
    primary key : 主键索引，加快查询速度, 列的值不能重复
    NOT NULL    标识该字段不能为空
    DEFAULT    为该字段设置默认值

例子1：
create table t1(
    id int,
    name char(5)
)charset=utf8;
Query OK, 0 rows affected (0.72 sec)   # 如果回显是queryok，代表创建成功

增加数据：

语法：
    insert into 表名 (列1, 列2) values (值1,'值2');
例子：
    insert into t1 (id, name) values (1, 'zekai');
    insert into t1 (id, name) values (1, 'zekai2');

查询数据：

语法：

select 列1, 列2 from 表名;  （*代表查询所有的列）

例子1：
    mysql> select * from t1;

    +------+-------+
    | id   | name  |
    +------+-------+
    |    1 | zekai |
    +------+-------+
    1 row in set (0.00 sec)

例子2:
create table t2(
    id int auto_increment primary key,
    name char(10) 
)charset=utf8;

insert into t2 (name) values ('zekai1');

例子3: (推荐)
create table t3(
    id  int unsigned auto_increment primary key,
    name char(10) not null default 'xxx',
    age int not null default 0
)charset=utf8;
                    
mysql> insert into t3 (age) values (10);
Query OK, 1 row affected (0.05 sec)
                        
mysql> select * from t3;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | xxx  |  10 |
+----+------+-----+

列类型： （********************）

create table 表名(
    字段名  列类型 unsigned [可选的参数],  ### 记住加逗号
    字段名  列类型 [可选的参数],  ### 记住加逗号
    字段名  列类型 [可选的参数]  ### 最后一行不加逗号
    .....
)charset=utf8;  #### 后面加分号

数字：

整型：

tinyint
smallint
int   （************************） 推荐使用
mediumint
bigint

​ a.整数类型
​ b.取值范围
​ c.unsigned 加上代表不能取负数 只适用于整型
​ 应用场景：根据公司业务的场景，来选取合适的类型

浮点型：

create table t5(
    id int auto_increment primary key,
    salary decimal(16,10),
    num float
)charset=utf8;

float: 不一定精确
decimal: 非常精确，decimal(6, 2) m是数字总个数（负号不算），d是小数点后位数。

正好 10 位：
mysql> insert into t5 (salary, num) values (500023.2312345678, 5000.2374837284783274832);
Query OK, 1 row affected (0.04 sec)

mysql> select * from t5;
+----+-------------------+---------+
| id | salary            | num     |
+----+-------------------+---------+
|  1 | 500023.2312345678 | 5000.24 |
+----+-------------------+---------+
1 row in set (0.00 sec)

少于10位：
mysql> insert into t5 (salary, num) values (500023.231234567, 5000.2374837284783274832);
Query OK, 1 row affected (0.04 sec)

mysql> select * from t5;
+----+-------------------+---------+
| id | salary            | num     |
+----+-------------------+---------+
|  1 | 500023.2312345678 | 5000.24 |
|  2 | 500023.2312345670 | 5000.24 |
+----+-------------------+---------+

多于10位：
mysql> insert into t5 (salary, num) values (500023.23123456789, 5000.2374837284783274832);
Query OK, 1 row affected, 1 warning (0.03 sec)
mysql> select * from t5;
+----+-------------------+---------+
| id | salary            | num     |
+----+-------------------+---------+
|  1 | 500023.2312345678 | 5000.24 |
|  2 | 500023.2312345670 | 5000.24 |
|  3 | 500023.2312345679 | 5000.24 |
+----+-------------------+---------+

字符串

char(长度) ： 定长

varchar(长度)：变长

create table t6(
    id  int auto_increment primary key,
    name char(10) not null default 'xxx',
)charset=utf8;

create table t6(
    id  int auto_increment primary key,
    name varchar(10) not null default 'xxx'
)charset=utf8;

mysql> insert into t6 (name) values ('hello');
Query OK, 1 row affected (0.03 sec)

mysql> select * from t6;
+----+-------+
| id | name  |
+----+-------+
|  1 | hello |
+----+-------+
1 row in set (0.00 sec)

mysql> insert into t6 (name) values ('hellodb');

区别：

char: 定长，

无论插入的字符是多少个，永远固定占规定的长度

场景：

​ 身份证

​ 手机号 char(11)

​ md5加密之后的值，比如密码 等 char(32)

varchar: 变长，

根据插入的字符串的长度来计算所占的字节数，但是有一个字节是用来保存字符串的大小的

注意：如果， 不能确定插入的数据的大小， 一般建议使用 varchar(255)

时间日期类型

    YEAR: YYYY（1901/2155）
    DATE: YYYY-MM-DD（1000-01-01/9999-12-31）
    TIME: HH:MM:SS（'-838:59:59'/'838:59:59'）

    DATETIME  (***************************)
        YYYY-MM-DD: HH:MM:SS（1000-01-01 00:00:00/9999-12-31 23:59:59 
    TIMESTAMP:  YYYYMMDD HHMMSS（1970-01-01 00:00:00/2037 年某时）

例子：
create table t8(
    d date,
    t time,
    dt datetime
);  
mysql> insert into t8 values(now(),now(),now());
Query OK, 1 row affected, 1 warning (0.08 sec)

mysql> select * from t8;
+------------+----------+---------------------+
| d          | t        | dt                  |
+------------+----------+---------------------+
| 2019-10-29 | 10:49:51 | 2019-10-29 10:49:51 |
+------------+----------+---------------------+
1 row in set (0.00 sec)
insert into t8 values(now(),now(),now());

枚举

列出所有的选项
create table t9 (
    id int auto_increment primary key,
    gender enum('male','female')
)charset utf8;
                
mysql> insert into t9 (gender) values ('male');
Query OK, 1 row affected (0.04 sec)

mysql> insert into t9 (gender) values ('female');
Query OK, 1 row affected (0.03 sec)

mysql> insert into t9 (gender) values ('dshajjdsja');

改

1. 修改表名
    ALTER TABLE 旧表名 RENAME 新表名;
        
    mysql> alter table t8 rename t88;
    Query OK, 0 rows affected (0.19 sec)
        
2. 增加字段
    ALTER TABLE 表名
    ADD 字段名 列类型 [可选的参数],
    ADD 字段名 列类型 [可选的参数];
        
    mysql> alter table t88 add name varchar(32) not null default '';
    Query OK, 0 rows affected (0.82 sec)
    Records: 0  Duplicates: 0  Warnings: 0
        
上面添加的列永远是添加在最后一列之后,还可以添加到最前面

    ALTER TABLE 表名
    ADD 字段名 列类型 [可选的参数] FIRST;
        
    mysql> alter table t88 add name3 varchar(32) not null default '' first;
    Query OK, 0 rows affected (0.83 sec)
    Records: 0  Duplicates: 0  Warnings: 0

    ALTER TABLE 表名
    ADD 字段名 列类型 [可选的参数] AFTER 字段名;
    mysql> alter table t88 add name4 varchar(32) not null default '' after d;
    Query OK, 0 rows affected (0.68 sec)
    Records: 0  Duplicates: 0  Warnings: 0
            
3. 删除字段
    ALTER TABLE 表名  DROP 字段名;
            
    mysql> alter table t88 drop name4;
    Query OK, 0 rows affected (0.66 sec)
    Records: 0  Duplicates: 0  Warnings: 0

4. 修改字段
    ALTER TABLE 表名 MODIFY 字段名 数据类型 [完整性约束条件…];
            
    mysql> alter table t88 modify name2 char(20);
    Query OK, 1 row affected (0.88 sec)
    Records: 1  Duplicates: 0  Warnings: 0
    
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…];
            
mysql> alter table t88 change name2 name22 varchar(32) not null default '';
    Query OK, 1 row affected (0.82 sec)
    Records: 1  Duplicates: 0  Warnings: 0  
            
    mysql> alter table t88 change name22 name23;

删

    drop table 表名;  #### 线上禁用
    mysql> drop table t9;
    Query OK, 0 rows affected (0.18 sec)

查

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t1             |
+----------------+
1 row in set (0.00 sec)

复制表结构

mysql> create table t89 like t88;
Query OK, 0 rows affected (0.33 sec)

二. 操作表数据行：

增加数据：

语法：
    insert into 表名 (列1, 列2) values (值1,'值2');
例子：
    insert into t1 (id, name) values (1, 'zekai');
    insert into t1 (id, name) values (1, 'zekai2');
    insert into t1 (id, name) values (1, 'zekai2'),(2, 'zekai3'),(3,'zekai4');
    
# 暴力复制
mysql> insert into t66 (name) select name from t6;
Query OK, 4 rows affected (0.09 sec)
Records: 4  Duplicates: 0  Warnings: 0

删

delete from 表名 where 条件;

mysql> delete from t5 where id=1;
mysql> delete from t5 where id>1;
mysql> delete from t5 where id>=1;
mysql> delete from t5 where id<1;
mysql> delete from t5 where id<=1;
mysql> delete from t5 where id>=1 and id<10;
Query OK, 1 row affected (0.06 sec)
            
delete from 表名; 删除表中所有的数据
            
mysql> insert into t5 (salary, num) values (500023.2312345679,  5000.24);
Query OK, 1 row affected (0.08 sec)

mysql> select * from t5;
+----+-------------------+---------+
| id | salary            | num     |
+----+-------------------+---------+
|  4 | 500023.2312345679 | 5000.24 |
+----+-------------------+---------+
1 row in set (0.00 sec)

truncate 表名; # 没有where条件的

mysql> truncate t5;
Query OK, 0 rows affected (0.25 sec)

mysql> select * from t5;
Empty set (0.00 sec)

mysql> insert into t5 (salary, num) values (500023.2312345679,  5000.24);
Query OK, 1 row affected (0.06 sec)

mysql> select * from t5;
+----+-------------------+---------+
| id | salary            | num     |
+----+-------------------+---------+
|  1 | 500023.2312345679 | 5000.24 |
+----+-------------------+---------+
1 row in set (0.00 sec)

区别：

1、delete之后，插入数据从上一次主键自增加1开始， truncate则是从1开始

2、delete删除， 是一行一行的删除， truncate：全选删除 truncate删除的速度是高于delete的

改

        update 表名 set 列名1=新值1,列名2=新值2 where 条件;
        mysql> update t66 set name='xxxx' where id=30;
        Query OK, 1 row affected (0.04 sec)
        Rows matched: 1  Changed: 1  Warnings: 0
    
        mysql> update t66 set name='xxxx' where id<30;
        mysql> update t66 set name='xxxx' where id<=30;
        mysql> update t66 set name='xxxx' where id>=30;
        mysql> update t66 set name='xxxx' where id>30;
        mysql> update t66 set name='xxxx' where id>20 and id<32;
        mysql> update t66 set name='xxxx' where id>20 or name='zekai';
        
        Query OK, 1 row affected (0.04 sec)
        Rows matched: 1  Changed: 1  Warnings: 0

查

语法：

    select 列1, 列2 from 表名;  （*代表查询所有的列）
    select * from 表名;  （*代表查询所有的列）
    select * from t66 where id>30 and id<40;
    select * from t66 where id>30;
    select * from t66 where id<30;
    select * from t66 where id<=30;
    select * from t66 where id>=30;
    select * from t66 where id!=30;
    select * from t66 where id<>30;
    mysql> select * from t1;
    +------+-------+
    | id   | name  |
    +------+-------+
    |    1 | zekai |
    +------+-------+
    1 row in set (0.00 sec) 
            

between..and...: 取值范围是闭区间
            
    select * from t66 where id between 30 and 40;
    mysql> select * from t66 where id between 31 and 33;
    +----+--------+
    | id | name   |
    +----+--------+
    | 31 | dsadsa |
    | 32 | dsadsa |
    | 33 | dsadsa |
    +----+--------+
        
避免重复DISTINCT
    mysql> select distinct name from t66;
    +--------+
    | name   |
    +--------+
    | xxxx   |
    | hds    |
    | dsadsa |
    +--------+
    3 rows in set (0.00 sec)
            
通过四则运算查询 （不要用）
    mysql> select name, age*10 from t3;
    +------+--------+
    | name | age*10 |
    +------+--------+
    | xxx  |    100 |
    +------+--------+
    1 row in set (0.01 sec)

    mysql> select name, age*10 as age from t3;
    +------+-----+
    | name | age |
    +------+-----+
    | xxx  | 100 |
    +------+-----+
    1 row in set (0.02 sec)
            
in(80,90,100):
            
    mysql> select * from t66 where id in (23,34,11);
    +----+------+
    | id | name |
    +----+------+
    | 11 | xxxx |
    | 23 | hds  |
    +----+------+
    2 rows in set (0.04 sec)
            
like : 模糊查询
    以x开头：
        mysql> select * from t66 where name like 'x%';
        +----+------+
        | id | name |
        +----+------+
        |  1 | xxxx |
        |  2 | xxxx |
        |  3 | xxxx |
        |  4 | xxxx |
        |  8 | xxxx |
        |  9 | xxxx |
        | 10 | xxxx |
        | 11 | xxxx |
        | 15 | xxxx |
        | 16 | xxxx |
        | 17 | xxxx |
        | 18 | xxxx |
        | 30 | xxxx |
        +----+------+
        13 rows in set (0.05 sec)
                
    以x结尾：
        mysql> select * from t66 where name like '%x';
        +----+------+
        | id | name |
        +----+------+
        |  1 | xxxx |
        |  2 | xxxx |
        |  3 | xxxx |
        |  4 | xxxx |
        |  8 | xxxx |
        |  9 | xxxx |
        | 10 | xxxx |
        | 11 | xxxx |
        | 15 | xxxx |
        | 16 | xxxx |
        | 17 | xxxx |
        | 18 | xxxx |
        | 30 | xxxx |
        +----+------+
        13 rows in set (0.00 sec)
            
    包含x的：
mysql> select * from t66 where name like '%x%';