目录
一、数据表（文件）：
1.1增
1.1.1列表的创建：
create table 表名（字段名 列约束 [可选的参数] , ### 记住加逗号
字段名 列约束 [可选的参数] , ### 记住加逗号
字段名 列约束 [可选的参数] ### 最后一行不加逗号
）charset=utf-8; ### 后面加分号
例子：
create table t1(
id int,
name char(5)
)charset=utf-8;
1.1.2增加数据：
insert into 表明 (列1,,列2) values (值1,'值2');
例子：insert into u1(id ,name) values(1,'guanghao');
inster into u2(id,name) values(1,'guanghao1');
1.2查看表内数据
select 列1,列2 from 表名;(*代表查询所有的列)
例子：
mysql> select id,name from u1; +------+-----------+ | id | name | +------+-----------+ | 1 | guanghao | | 1 | guanghao1 | +------+-----------+ 2 rows in set (0.00 sec)
例子2：
mysql> create table u2(
-> id int auto_increment primary key,
-> name char(10)
-> )charset=utf8;
Query OK, 0 rows affected (0.31 sec)
mysql> insert into u2(name) values('guanghao');
Query OK, 1 row affected (0.05 sec)
mysql> select * from u2;
+----+----------+
| id | name |
+----+----------+
| 1 | guanghao |
+----+----------+
1 row in set (0.00 sec)
例子3（推荐使用这种方法）：
mysql> create table u3(
-> name char(10) not null default 'xxx',
-> id int unsigned auto_increment primary key,
-> age int not null default 0
-> )charset=utf8;
Query OK, 0 rows affected (0.32 sec)
mysql> insert into u3(age) values (10);
Query OK, 1 row affected (0.06 sec)
mysql> select * from u3;
+------+----+-----+
| name | id | age |
+------+----+-----+
| xxx | 1 | 10 |
+------+----+-----+
1 row in set (0.00 sec)
1.3改
1.3.1修改表名
alter table 旧表名 rename 新表名；
mysql> alter table u6 rename hello; Query OK, 0 rows affected (0.16 sec)
1.3.2增加字段
方式一
alter table 表名 add 字段名 列类型 [可选参数]，add 字段名 列类型[可选参数]；
这种方式添加的列默认添加到最后一列的后面。
mysql> alter table hello add name varchar(32) not null default ''; Query OK, 0 rows affected (0.80 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from hello; +----+--------+------+ | id | gender | name | +----+--------+------+ | 1 | female | | | 2 | male | | +----+--------+------+ 2 rows in set (0.00 sec)
方式二
alter table 表名 add 字段名 列类型 [可选参数] first；
添加到第一列的前面。
mysql> alter table hello add age int first; Query OK, 0 rows affected (0.52 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from hello; +------+----+--------+------+ | age | id | gender | name | +------+----+--------+------+ | NULL | 1 | female | | | NULL | 2 | male | | +------+----+--------+------+
方式三
alter table 表名 add 字段名 列类型 [可选参数] after 字段名；
添加到某一列的后面。
mysql> alter table hello add age1 int not null default 0 after age; Query OK, 0 rows affected (0.68 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from hello; +------+------+----+--------+------+ | age | age1 | id | gender | name | +------+------+----+--------+------+ | NULL | 0 | 1 | female | | | NULL | 0 | 2 | male | | +------+------+----+--------+------+ 2 rows in set (0.00 sec)
1.3.3删除字段
alter table 表名 drop 字段名 ；
mysql> alter table hello drop age; Query OK, 0 rows affected (1.70 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from hello; +------+----+--------+------+ | age1 | id | gender | name | +------+----+--------+------+ | 0 | 1 | female | | | 0 | 2 | male | | +------+----+--------+------+ 2 rows in set (0.00 sec)
1.3.4修改字段
1.修改字段的数据类型
alter table 表名 modify 字段名 数据类型 [完整性约束条件]；
mysql> alter table hello modify name char(10); Query OK, 2 rows affected (0.98 sec) Records: 2 Duplicates: 0 Warnings: 0
2.修改字段名和数据类型
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 hello change age1 age; 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 #不能只改字段名而不指定数据类型，否则会报错 mysql> alter table hello change age1 age int not null default 1; Query OK, 0 rows affected (0.11 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from hello; +-----+----+--------+------+ | age | id | gender | name | +-----+----+--------+------+ | 0 | 1 | female | | | 0 | 2 | male | | +-----+----+--------+------+ 2 rows in set (0.00 sec)
1.4删除列表
删除表语法：drop table 表名；（注意慎用，线上禁止使用）
mysql> show tables; +-----------------+ | Tables_in_test2 | +-----------------+ | hello | | t1 | | t2 | | t3 | | t4 | | t5 | | t6 | | t7 | | u1 | | u2 | | u3 | | u4 | | u5 | +-----------------+ 13 rows in set (0.04 sec) mysql> drop table u5; Query OK, 0 rows affected (0.17 sec) mysql> show tables; +-----------------+ | Tables_in_test2 | +-----------------+ | hello | | t1 | | t2 | | t3 | | t4 | | t5 | | t6 | | t7 | | u1 | | u2 | | u3 | | u4 | +-----------------+ 12 rows in set (0.00 sec)
1.5查看库内列表及表结构
方式一
show tables；查看该数据库内所有的列表
方式二
show create table 表名；查看具体表结构的详细信息
mysql> show create table hello;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| hello | CREATE TABLE `hello` (
`age` int(11) NOT NULL DEFAULT '1',
`id` int(11) NOT NULL AUTO_INCREMENT,
`gender` enum('male','female') DEFAULT NULL,
`name` char(10) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
1.6复制表结构
方式一
show create table 表名；查看具体表结构的详细信息然后手动复制过来，在创建新表。
方式二
create table 新表名 like 被复制的表名；需要强调的是，这里的复制仅仅是复制表的结构，而不复制表的内容，新表示一个空表。
mysql> create table hello1 like hello;
Query OK, 0 rows affected (0.32 sec)
mysql> show create table hello1;
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| hello1 | CREATE TABLE `hello1` (
`age` int(11) NOT NULL DEFAULT '1',
`id` int(11) NOT NULL AUTO_INCREMENT,
`gender` enum('male','female') DEFAULT NULL,
`name` char(10) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
二、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
2.1数字
2.1.1整型
tinyint
smallint
int（*********）
mediumint
bigint
整数类型
取值范围
一个字节占8位，int占4个字节
在整数类型上加上
unsigned 代表不能取负数，不加是有符号的，且unsigned只适用于整型，且必须在数据类型前面。
数据类型前面。
根据应用场景：根据公司的业务场景，选择合适的类型。
2.1.2浮点型（*********）
float：一共只有四个字节，如果整数部分过长，则小数部分精确的位数会逐渐减少。
decimal：可以精确到设定的位数， decimal(m, d) m是数字总个数（负号不算），d是精确到小数点后多少位。
例子：
mysql> create table u4( -> id int auto_increment primary key, -> salary decimal(15,10), -> num float -> )charset=utf8; Query OK, 0 rows affected (0.31 sec) mysql> insert into u4(salary,num) alues(15000.12345678913579,15000.12345678913579); Query OK, 1 row affected, 1 warning (0.15 sec) mysql> select * from u4; +----+------------------+---------+ | id | salary | num | +----+------------------+---------+ | 1 | 15000.1234567891 | 15000.1 | +----+------------------+---------+ 1 row in set (0.00 sec) mysql> insert into u4(num) values(3.1415926); Query OK, 1 row affected (0.10 sec) mysql> select * from u4; +----+------------------+---------+ | id | salary | num | +----+------------------+---------+ | 1 | 15000.1234567891 | 15000.1 | | 2 | NULL | 3.14159 | +----+------------------+---------+
2.2字符串
char与varchar
char是定长的，无论插入的字符是多少个，永远固定占规定的长度；varchar是变长的，根据掺入的字符串长度计算所占的字节数，它所占的内存中有一个字节用来存储字符串的大小。
注意：如果在某些情况下不能确定数据的大小，建议使用varchar(255)。
char一般应用于固定长度的数据，如身份证、手机号、MD5加密之后的值。
| Value | CHAR(4) |
Storage Required | VARCHAR(4) |
Storage Required |
|---|---|---|---|---|
'' |
' ' |
4 bytes | '' |
1 byte |
'ab' |
'ab ' |
4 bytes | 'ab' |
3 bytes |
'abcd' |
'abcd' |
4 bytes | 'abcd' |
5 bytes |
'abcdefgh' |
'abcd' |
4 bytes | 'abcd' |
5 bytes |
2.3时间日期类型
year精确到年
time只显示时分秒
date只显示到日期
datetime(*********)年月日时分秒（这个是最常用的，其他的时间类型基本不用）
timestamp时间戳
例子：
mysql> create table u5(d date,t time,dt datetime); Query OK, 0 rows affected (0.46 sec) mysql> insert into u5 values(now(),now(),now());#这里调用了new()函数 Query OK, 1 row affected, 1 warning (0.13 sec) mysql> select * from u5; +------------+----------+---------------------+ | d | t | dt | +------------+----------+---------------------+ | 2019-10-29 | 15:08:42 | 2019-10-29 15:08:42 | +------------+----------+---------------------+ 1 row in set (0.00 sec)
2.4枚举ENUM
枚举就是限定输入该列的内容必修是已经对定好的几个选项中的一个，比如设定好性别一栏只能输入男或女。
ENUM对1-255个成员的枚举需要1个字节存储;对于255-65535个成员，需要2个字节存储;最多允许65535个成员，只能单选。
例子：
mysql> create table u6 (id int auto_increment primary key,
-> gender enum('male','female')
-> )charset utf8;
Query OK, 0 rows affected (0.44 sec)
mysql> insert into u6(gender) values ('female');
Query OK, 1 row affected (0.07 sec)
mysql> insert into u6(gender) values('male');
Query OK, 1 row affected (0.06 sec)
mysql> insert into u6(gender) values('123');
ERROR 1265 (01000): Data truncated for column 'gender' at row 1
三、操作表数据行
3.1增加表中的数据
语法 insert into 表名（列1，列2） values (值1，‘值2’)；
值如果是字符串类型则需要加引号。
mysql> insert into hello(age,gender,name) values(18,'male','zgh'); Query OK, 1 row affected (0.05 sec) mysql> select * from hello; +-----+----+--------+------+ | age | id | gender | name | +-----+----+--------+------+ | 0 | 1 | female | | | 0 | 2 | male | | | 18 | 3 | male | zgh | +-----+----+--------+------+ 3 rows in set (0.00 sec)
3.2 删除表中的数据
3.2.1删除表内具体的数据
delete from 表名 where 条件；
这里的条件可以是与或非和比较运算的组合。
mysql> delete from hello where id=1; Query OK, 1 row affected (0.14 sec) mysql> delete from hello where id<=2 and id=3; Query OK, 0 rows affected (0.00 sec)
3.2.2删除整个表所有的数据
1.delete from 表名；
mysql> delete from u4; Query OK, 3 rows affected (0.06 sec) mysql> show create table u4; +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | u4 | CREATE TABLE `u4` ( `id` int(11) NOT NULL AUTO_INCREMENT, `salary` decimal(15,10) DEFAULT NULL, `num` float DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) mysql> select * from u4; Empty set (0.00 sec)
2.truncate 表名；
mysql> select * from u4; Empty set (0.00 sec) mysql> truncate u3; Query OK, 0 rows affected (0.32 sec) mysql> select * from u3; Empty set (0.00 sec)
delete 和truncate的区别：
1.delete之后，如果重新往表里插入数据，数据会从上一次主键自增加1开始（如果有某一列设置了自增加）而truncate则是从1开始。
如下例就是通过delete清空的列表由于id设置的自增加，所以，清空后再次插入新的数据，仍会接着之前的id创建新的id。
mysql> insert into u4(salary) values(10000); Query OK, 1 row affected (0.06 sec) mysql> select * from u4; +----+------------------+------+ | id | salary | num | +----+------------------+------+ | 4 | 10000.0000000000 | NULL | +----+------------------+------+ 1 row in set (0.00 sec)
使用truncate清空列表
mysql> truncate u4; Query OK, 0 rows affected (0.31 sec) mysql> insert into u4(salary) values(10000); Query OK, 1 row affected (0.05 sec) mysql> select * from u4; +----+------------------+------+ | id | salary | num | +----+------------------+------+ | 1 | 10000.0000000000 | NULL | +----+------------------+------+ 1 row in set (0.00 sec)
2.delete是一行一行删除的，truncate是全选删除；truncate删除的速度是高于delete。
3.3对列表中的某个值进行修改
update 表名 set 列名1=新值，列名2=新值 where 条件；
mysql> select *from u4; +----+------------------+----------+ | id | salary | name | +----+------------------+----------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | | 5 | 15000.0000000000 | xxxx | | 6 | 8000.0000000000 | xiaoming | | 7 | 9000.0000000000 | xiaoming | +----+------------------+----------+ 7 rows in set (0.00 sec) mysql> update u4 set salary=10000 where name='xiaoming' and id=4; Query OK, 0 rows affected (0.02 sec) Rows matched: 0 Changed: 0 Warnings: 0 mysql> select *from u4; +----+------------------+----------+ | id | salary | name | +----+------------------+----------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | | 5 | 15000.0000000000 | xxxx | | 6 | 8000.0000000000 | xiaoming | | 7 | 9000.0000000000 | xiaoming | +----+------------------+----------+ 7 rows in set (0.00 sec)
3.4查询表中的元素
3.4.1select 列1 ，列2 from表名；查询表中的指定列
3.4.2select * from 表名；*代表查询所有的列
3.4.3select * from 表名 where 条件；按条件查询
mysql> select *from u4; +----+------------------+----------+ | id | salary | name | +----+------------------+----------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | | 5 | 15000.0000000000 | xxxx | | 6 | 8000.0000000000 | xiaoming | | 7 | 9000.0000000000 | xiaoming | +----+------------------+----------+ 7 rows in set (0.00 sec) mysql> select * from u4 where id<5; +----+------------------+------+ | id | salary | name | +----+------------------+------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | +----+------------------+------+ 4 rows in set (0.02 sec)
3.4.4select * from 表名 where 列名 between 条件1 and 条件2；
取值范围是闭区间
mysql> select * from u4 where id between 1 and 4; +----+------------------+------+ | id | salary | name | +----+------------------+------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | +----+------------------+------+ 4 rows in set (0.05 sec)
3.4.5避免重复查询distinct
mysql> select distinct salary from u4; +------------------+ | salary | +------------------+ | 10000.0000000000 | | 12000.0000000000 | | 14000.0000000000 | | 15000.0000000000 | | 8000.0000000000 | | 9000.0000000000 | +------------------+ 6 rows in set (0.04 sec)
3.4.6四则运算查询（不要用，效率太低）
mysql> select id,salary*10 from u4; +----+-------------------+ | id | salary*10 | +----+-------------------+ | 1 | 100000.0000000000 | | 2 | 100000.0000000000 | | 3 | 120000.0000000000 | | 4 | 140000.0000000000 | | 5 | 150000.0000000000 | | 6 | 80000.0000000000 | | 7 | 90000.0000000000 | +----+-------------------+ 7 rows in set (0.03 sec)
3.4.7模糊查询like（效率也低）
以某个字符开头：
mysql> select * from u4 where name like 'x%';#这里的百分号指后面可以为任意字符 +----+------------------+----------+ | id | salary | name | +----+------------------+----------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | | 5 | 15000.0000000000 | xxxx | | 6 | 8000.0000000000 | xiaoming | | 7 | 9000.0000000000 | xiaoming | +----+------------------+----------+ 7 rows in set (0.02 sec)
以某个字符结尾：
mysql> select * from u4 where name like '%x';#这里的百分号指x前面可以为任意字符 +----+------------------+------+ | id | salary | name | +----+------------------+------+ | 1 | 10000.0000000000 | xxxx | | 2 | 10000.0000000000 | xxxx | | 3 | 12000.0000000000 | xxxx | | 4 | 14000.0000000000 | xxxx | | 5 | 15000.0000000000 | xxxx | +----+------------------+------+ 5 rows in set (0.00 sec)
包含某个字符：
mysql> select * from u4 where name like '%a%';#这里的百分号指a前面后面可以为任意字符 +----+-----------------+----------+ | id | salary | name | +----+-----------------+----------+ | 6 | 8000.0000000000 | xiaoming | | 7 | 9000.0000000000 | xiaoming | +----+-----------------+----------+ 2 rows in set (0.00 sec)