系统数据库
information_schema; 虚拟库，主要存储了系统中一些数据库对象信息。
performance_schema: 主要存储数据库的性能参数
mysql:授权库，主要存储系统用户的权限信息
sys:主要存储数据库服务器性能参数
（目标是把performance_schema的把复杂度降低）
1. mysql -uroot -pQianfeng@123 -e "create database db2 default charset 'utf8'"
2. 直接去创建数据库目录并且修改权限
3. mysql> create database school;
数据库命名规则：
区分大小写
唯一性
不能使用关键字如 create SELECT
不能单独使用数字
不要使用中文
查看数据库
mysql> show databases; //查看所有数据库
mysql> show create database school; //查看创建的库信息
mysql> SELECT database(); //查看当前库
切换数据库
mysql> use school
mysql> show tables;
创建表 create table
查看表结构 desc table_name, show create table
表完整性约束
修改表 alter table
复制表 create table ...
删除表 drop table
命令行操作数据库（脚本）
mysql>create database db2;
mysql>use db2
mysql>create table t1(name varchar(50),age int);
# mysql -u root -p1 -e "create database school"
# mysql -u root -p1 -e "use school;create table t2(name char(20),age int(3))"
在mysql客户端内执行系统命令
mysql> system ls
mysql> \! ls
exit
语法：
create table 表名(
字段名1 类型[(宽度) 约束条件],
字段名2 类型[(宽度) 约束条件],
字段名3 类型[(宽度) 约束条件]
)[存储引擎 字符集];
==在同一张表中，字段名是不能相同
==宽度和约束条件可选
==字段名和类型是必须的
mysql> CREATE DATABASE school;
mysql> use school;
mysql> create table student1(
-> id int,
-> name varchar(50),
-> sex enum('male','female'),
-> age int
-> );
Query OK, 0 rows affected (0.03 sec)
查看表（当前所在库）
mysql> show tables;
+------------------+
| Tables_in_school |
+------------------+
| student1 |
+------------------+
1 row in set (0.00 sec)
mysql> desc student1; //查看表结构
mysql> show create table student1;
mysql> show table status like 'student1' \G 显示数据的详细信息
查看表内容
mysql> SELECT id,name,sex,age from student1; //查询表中指定字段的值
Empty set (0.00 sec)
mysql> SELECT * from student1; //查询表中所有字段的值
Empty set (0.00 sec)
mysql> SELECT name,age from student1; //查询表中指定字段的值
Empty set (0.00 sec)
修改表：
alter 修改表名称 修改字段名称 修改字段数据类型 修改字段的修饰符
insert 插入数据
delete 删除数据
update 更新数据
修改表名称
mysql> rename table emp to abc;
mysql> alter table abc rename emp;
添加新字段
mysql> create table t1(id int(5),name varchar(20));
mysql> alter table t1 add math int(10);
mysql> alter table t1 add (chinese int(10),english int(10));
修改字段修饰符（约束）
mysql> alter table t1 modify chinese int(5) not null;
修改字段名称、数据类型、修饰符（约束）
mysql> alter table t1 change chinese china int(6);
mysql> alter table t1 change english en int(6) after id;
mysql> alter table t1 change en en int(6) after name;
mysql> alter table t1 modify en int(6) after name;
mysql> alter table t1 modify en int(6) first;
mysql> alter table t1 modify en int(6) after id;
删除字段
mysql> alter table t1 drop en;
插入数据(添加记录)
字符串必须引号引起来
mysql> insert into t1(id,name,math,china) values(1,"wing",80,90);
mysql> insert into t1(id,name,math,china) values(2,"king",70,100),(3,"tom",50,70);
mysql> insert into t1 values(4,"xiaosan",50,100);
mysql> insert into t1(id,math) values(5,70);
mysql> insert into t1 set id=6,math=65;
更新记录
mysql> update t1 set name="lili" WHERE id=5;
删除记录
mysql> delete from t1 WHERE id=6;
mysql> delete from t1; //删除所有记录
表复制：
复制一张表
mysql> create table t10(SELECT * from t3);
mysql> create table t10(SELECT id,name from t3);
复制表结构
mysql> desc t3;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id1 | int(11) | YES | | NULL | |
| id2 | int(6) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> create table t13(SELECT id1,id2 from t3 WHERE 5=4);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t13;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id1 | int(11) | YES | | NULL | |
| id2 | int(6) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> create table t14(SELECT id1 from t3 WHERE 5=4);#将表的数据备份 不成立的
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t14;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id1 | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql> create table t4(SELECT * from t3 WHERE 5=4);
mysql> create table t4(SELECT id,name from t3 WHERE 5=4);
复制记录
mysql> insert into t3 SELECT * from t10 WHERE id=9; 俩表格字段要相同
删除表
mysql> drop table t1;
删除库
mysql> drop database newrain;
了解(！！！)
表完整性约束
作用：用于保证数据的完整性和一致性
==============================================================
约束条件 说明
NOT NULL 标识该字段不能为null
UNIQUE KEY (UK) 标识该字段的值是唯一的，可以为空，一个表中可以有多个UNIQUE KEY
AUTO_INCREMENT 标识该字段的值自动增长（整数类型，而且为主键）
DEFAULT 为该字段设置默认值
UNSIGNED 无符号(正数)
ZEROFILL 使用0填充，例如0000001
说明：
1. 是否允许为空，默认NULL；可设置NOT NULL，字段不允许为空，必须赋值
2. 字段是否有默认值，缺省的默认值是NULL，如果插入记录时不给字段赋值，此字段使用默认值
sex enum('male','female') not null default 'male'
age int unsigned NOT NULL default 20 必须为正值（无符号） 不允许为空 默认是20
数值类型：
整数类型 TINYINT SMALLINT MEDIUMINT INT BIGINT
整型可以指定是有符号的和无符号的，默认是有符号的
可以通过UNSIGNED来说明某个字段是无符号的。
浮点数类型 FLOAT DOUBLE
字符串类型：
CHAR系列 CHAR VARCHAR
BINARY系列 BINARY VARBINARY #二进制
枚举类型： ENUM
集合类型： SET
时间和日期类型：
DATE TIME DATETIME TIMESTAMP YEAR
===整数类型测试：tinyint(有符号型最大值127),int（有符号型最大值2147483647)
作用：用于存储用户的年龄、游戏的Level、经验值等。
LAB1(案例1):
mysql> create database db1;
mysql> use db1;
mysql> create table test1(
-> tinyint_test tinyint,
-> int_test int
-> );
mysql> desc test1;
+--------------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------+------+-----+---------+-------+
| tinyint_test | tinyint(4) | YES | | NULL | |
| int_test | int(11) | YES | | NULL | |
+--------------+------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> insert into test1 values (111,111);
Query OK, 1 row affected (0.09 sec)
mysql> insert into test1(tinyint_test) values( );
ERROR 1264 (22003): Out of range value for column 'tinyint_test' at row 1
mysql> insert into test1(int_test) values(2147483647);
Query OK, 1 row affected (0.05 sec)
mysql> insert into test1(int_test) values(2147483648);
ERROR 1264 (22003): Out of range value for column 'int_test' at row 1
//测试结果，默认有符号，超过存储范围出错。
LAB2: 无符号整型测试
mysql> create table test2(
-> tinyint_test tinyint unsigned, //约束条件unsigned限定只能存正值（无符号）
-> int_test int unsigned
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> desc test2;
+--------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------------------+------+-----+---------+-------+
| tinyint_test | tinyint(3) unsigned | YES | | NULL | |
| int_test | int(10) unsigned | YES | | NULL | |
+--------------+---------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into test2(tinyint_test) values(111);
Query OK, 1 row affected (0.06 sec)
mysql> insert into test2(int_test) values(2147483648);
Query OK, 1 row affected (1.87 sec)
mysql> insert into test2 values(-20,-20);
ERROR 1264 (22003): Out of range value for column 'tinyint_test' at row 1
测试整数类型的显示宽度（int不限制宽度）
mysql> create table t1 (
-> id1 int,
-> id2 int(6)
-> );
mysql> desc t1;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id1 | int(11) | YES | | NULL | |
| id2 | int(6) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
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> create table t2 (
-> id1 int zerofill,
-> id2 int(6) zerofill
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> desc t2;
+-------+---------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------------------+------+-----+---------+-------+
| id1 | int(10) unsigned zerofill | YES | | NULL | |
| id2 | int(6) unsigned zerofill | YES | | NULL | |
+-------+---------------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into t2 values(2,2);
Query OK, 1 row affected (0.01 sec)
mysql> SELECT * from t2;
+------------+--------+
| id1 | id2 |
+------------+--------+
| 0000000002 | 000002 |
+------------+--------+
1 row in set (0.00 sec)
mysql> insert into t2 values(3,2222222); //插入大于宽度限制的值，仍然可以存储
Query OK, 1 row affected (0.03 sec)
mysql> SELECT * from t2;
+------------+---------+
| id1 | id2 |
+------------+---------+
| 0000000002 | 000002 |
| 0000000003 | 2222222 |
+------------+---------+
2 rows in set (0.00 sec)
结论：整型的宽度仅为显示宽度，不是限制。因此建议整型无须指定宽度。
===浮点数类型测试：
作用：用于存储用户的身高、体重、薪水等
浮点数和定点数都可以用类型名称后加(M,D)的方式来表示，(M,D)表示一共显示M位数字（整数位
+小数位），其中D位于小数点后面，M和D又称为精度和标度。
?oat表示的精度大约是7位。
mysql> create table test4(float_test float(5,2)); //一共5位，小数占2位
Query OK, 0 rows affected (0.00 sec)
mysql> desc test4;
+------------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+------------+------+-----+---------+-------+
| float_test | float(5,2) | YES | | NULL | |
+------------+------------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql> insert into test4 values (10.2), (70.243), (70.246);
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> SELECT * from test4;
+------------+
| float_test |
+------------+
| 10.20 |
| 70.24 |
| 70.25 |
+------------+
3 rows in set (0.00 sec)
可以观察到，超出表示的范围，MySQL在保存值时会进行四舍五入。
mysql> insert into test4 values (1111.2);
ERROR 1264 (22003): Out of range value for column 'float_test' at row 1
mysql> create table t111(FROM1 float,FROM2 float(10,2));
mysql> insert into t111 values(123.123,12345678.90);
mysql> SELECT * from t111;
+---------+-------------+
| FROM1 | FROM2 |
+---------+-------------+
| 123.123 | 12345679.00 |
+---------+-------------+
注意：如果数据精度丢失，那么浮点型是按照四舍五入的方式进行计算
mysql> insert into t111 values(123.12345678,123456789.90);
ERROR 1264 (22003): Out of range value for column 'FROM2' at row 1
超出范围报错
mysql> insert into t111 values(123.12345678,99999999.99);
Query OK, 1 row affected (0.01 sec)
mysql> SELECT * from t111;
+---------+--------------+
| FROM1 | FROM2 |
+---------+--------------+
| 123.123 | 12345679.00 |
| 123.123 | 100000000.00 |
+---------+--------------+
2 rows in set (0.00 sec)
double（精度较高，更精确）精度有15位左右。
mysql> create table t112(
-> FROM1 double,
-> FROM2 double(10,2)
-> );
mysql> insert into t112 values(123.12345678,99999999.99);
mysql> SELECT * from t112;
+--------------+-------------+
| FROM1 | FROM2 |
+--------------+-------------+
| 123.12345678 | 99999999.99 |
+--------------+-------------+
1 row in set (0.00 sec)
定点数decimal测试（精度最高）：
mysql> create table test17(id int,a float(10,8),b decimal(10,8));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into test17 values (100,23.12345612,23.12345612);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * from test17;
+------+-------------+-------------+
| id | a | b |
+------+-------------+-------------+
| 100 | 23.12345695 | 23.12345612 |
+------+-------------+-------------+
1 row in set (0.00 sec)
注：?oat表示的精度大约是7位。
decimal整数大位数m为65。支持小数大位数d是30。
===时间和日期类型测试：year、date、time、datetime、timestamp
作用：用于存储用户的注册时间，文章的发布时间，文章的更新时间，员工的入职时间等
mysql> create table test_time(
-> d date,
-> t time,
-> dt datetime
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> desc test_time;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| d | date | YES | | NULL | |
| t | time | YES | | NULL | |
| dt | datetime | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
3 rows in set (0.01 sec)
mysql> SELECT now();
+---------------------+
| now() |
+---------------------+
| 2023-08-09 17:33:11 |
+---------------------+
1 row in set (0.00 sec)
mysql> insert into test_time values(now(),now(),now());
Query OK, 1 row affected, 1 warning (0.02 sec)
mysql> SELECT * from test_time;
+------------+----------+---------------------+
| d | t | dt |
+------------+----------+---------------------+
| 2023-08-09 | 17:33:47 | 2023-08-09 17:33:47 |
+------------+----------+---------------------+
1 row in set (0.00 sec)
timestamp
mysql> create table d(name char(20),time timestamp);
Query OK, 0 rows affected (0.01 sec)
mysql> insert into d values("laowang",null);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * from d;
+-----------+---------------------+
| name | time |
+-----------+---------------------+
| laowang | 2019-08-20 15:06:23 |
+-----------+---------------------+
1 row in set (0.00 sec)
注意事项：
其它的时间，按要求插入
==插入年份时，尽量使用4位值
==插入两位年份时，<=69，以20开头，比如65, 结果2065
>=70，以19开头，比如82，结果1982
mysql> create table t3(born_year year);
Query OK, 0 rows affected (0.40 sec)
mysql> desc t3;
+-----------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------+------+-----+---------+-------+
| born_year | year(4) | YES | | NULL | |
+-----------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql> insert into t3 values
-> (12),(80);
Query OK, 2 rows affected (0.06 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> SELECT * from t3;
+-----------+
| born_year |
+-----------+
| 2012 |
| 1980 |
+-----------+
2 rows in set (0.00 sec)
＝＝＝字符串类型测试：CHAR、VARCHAR
作用：用于存储用户的姓名、爱好、发布的文章等
CHAR 列的长度固定为创建表时声明的长度： 0 ~ 255
VARCHAR 列中的值为可变长字符串，长度： 0 ~ 65535
注：在检索的时候，CHAR列删除了尾部的空格，而VARCHAR则保留这些空格
mysql> create table vc (
-> v varchar(4),
-> c char(4)
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> desc vc;
+-------+------------+------+-----+---------+-------+
| 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 vc values('ab ','ab ');
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> SELECT * from vc;
+------+------+
| v | c |
+------+------+
| ab | ab |
+------+------+
1 row in set (0.00 sec)
mysql> SELECT length(v),length(c) from vc;
+-----------+-----------+
| length(v) | length(c) |
+-----------+-----------+
| 4 | 2 |
+-----------+-----------+
1 row in set (0.00 sec)
mysql> SELECT concat(v,'='), concat(c,'=') from vc; //在后面加字符'='，看的更清楚
+---------------+---------------+
| concat(v,'=') | concat(c,'=') |
+---------------+---------------+
| ab = | ab= |
+---------------+---------------+
1 row in set (0.00 sec)
字符串类型测试：BINARY、VARBINARY
BINARY 和 VARBINARY类似于CHAR 和 VARCHAR，不同的是它们包含二进制字符而不包含
非二进制字符串
mysql> create table binary_t (c binary(3));
mysql> insert into binary_t values ('10');
Query OK, 1 row affected (0.01 sec)
mysql> create table binary_d (c varbinary(3));
mysql> insert into binary_d values ('10');
Query OK, 1 row affected (0.01 sec)
mysql> SELECT length(c) from binary_t WHERE c=10;
+-----------+
| length(c) |
+-----------+
| 3 |
+-----------+
1 row in set, 2 warnings (0.01 sec)
mysql> SELECT length(c) from binary_d WHERE c=10;
+-----------+
| length(c) |
+-----------+
| 2 |
+-----------+
1 row in set (0.00 sec)
＝＝＝字符串类型
＝＝＝ENUM类型即枚举类型、集合类型SET测试
字段的值只能在给定范围中选择
常见的是单选按钮和复选框
enum 单选 只能在给定的范围内选一个值，如性别 sex 男male/女female
set 多选 在给定的范围内可以选择一个或一个以上的值（爱好1,爱好2,爱好3...）
表school.student3
姓名 name varchar(50)
性别 sex enum('m','FROM')
爱好 hobby set('music','book','game','disc')
mysql> use school
mysql> create table student3(
-> name varchar(50),
-> sex enum('m','FROM'),
-> hobby set('music','book','game','disc')
-> );
Query OK, 0 rows affected (0.31 sec)
mysql> desc student3;
+-------+-----------------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------------------+------+-----+---------+-------+
| name | varchar(50) | YES | | NULL | |
| sex | enum('m','FROM') | YES | | NULL | |
| hobby | set('music','book','game','disc') | YES | | NULL | |
+-------+-----------------------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> insert into student3 values
-> ('tom','m','book,game');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * from student3;
+------+------+-----------+
| name | sex | hobby |
+------+------+-----------+
| tom | boy | book,game |
+------+------+-----------+
1 row in set (0.00 sec)
mysql> insert into student3 values ('jack','m','play');
ERROR 1265 (01000): Data truncated for column 'hobby' at row 1
mysql> show create table student3\G
*************************** 1. row ***************************
Table: student3
Create Table: CREATE TABLE `student3` (
`name` varchar(50) default NULL,
`sex` enum('m','FROM') default NULL,
`hobby` set('music','book','game','disc') default NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1
在MySQL管理软件中，可以通过SQL语句中的DML语言来实现数据的操作，包括使用INSERT实现数据
的插入、DELETE实现数据的删除以及UPDATE实现数据的更新。
更新数据 insert
更新数据 update
删除数据 delete
一、插入数据INSERT
1. 插入完整数据（顺序插入）
语法一：
INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES (值1,值2,值3…值n);
语法二：
INSERT INTO 表名 VALUES (值1,值2,值3…值n);
2. 指定字段插入数据
语法：
INSERT INTO 表名(字段2,字段3…) VALUES (值2,值3…);
3. 插入多条记录
语法：
INSERT INTO 表名 VALUES
(值1,值2,值3…值n),
(值1,值2,值3…值n),
(值1,值2,值3…值n);
4. 插入查询结果
语法：
INSERT INTO 表1(字段1,字段2,字段3…字段n)
SELECT (字段1,字段2,字段3…字段n) FROM 表2
WHERE …;
例子：
mysql> create table student7(id int,name varchar(20),sex enum('m','FROM'),age int(2));
mysql> desc student7;
+-------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| sex | enum('m','FROM') | YES | | NULL | |
| age | int(2) | YES | | NULL | |
+-------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> insert into student7 values(1,'jack','m',20); \\顺序插入数据
mysql> insert into student7(name,age) values('bob',21); \\指定字段插入数据
mysql> insert into student7 values(6,'jex','m',21),(7,'bob1','FROM',22); \\插入多条记录
插入查询结果：
mysql> create table student_his(id int,name varchar(20),sex enum('m','FROM'),age int(2));
mysql> insert into student_his SELECT * from student7 WHERE name = 'bob'; \\插入查询结果
mysql> insert into student_his SELECT * from student7 WHERE age > 17; \\插入符合条件的
二、更新数据UPDATE
语法：
UPDATE 表名 SET 字段1=值1,字段2=值2 WHERE CONDITION;
示例：
mysql> update student7 set id=8; #修改全部
mysql> SELECT * from student7;
+------+------+------+------+
| id | name | sex | age |
+------+------+------+------+
| 8 | jex | m | 21 |
| 8 | bob1 | FROM | 22 |
+------+------+------+------+
2 rows in set (0.00 sec)
mysql> update student7 set id=9 WHERE name="bob1"; 指定条件
mysql> SELECT * from student7;
+------+------+------+------+
| id | name | sex | age |
+------+------+------+------+
| 8 | jex | m | 21 |
| 9 | bob1 | FROM | 22 |
+------+------+------+------+
2 rows in set (0.00 sec)
mysql> update student7 set id=10,name="newrain" WHERE name="bob1";
mysql> SELECT * from student7;
+------+----------+------+------+
| id | name | sex | age |
+------+----------+------+------+
| 8 | jex | m | 21 |
| 10 | newrain | FROM | 22 |
+------+----------+------+------+
2 rows in set (0.01 sec)
三、删除数据DELETE
语法：
DELETE FROM 表名
WHERE CONITION;
示例：
DELETE FROM mysql.user
WHERE authentication_string=’’;
delete from 表名 WHERE 条件;
mysql> delete from student7 WHERE name="jack";
delete from 表名; //删除表的全部数据
mysql> delete from student7;
Query OK, 3 rows affected (0.00 sec)
mysql> SELECT * from student7;
Empty set (0.01 sec)
| 字段解析 | 字段名 | 字段类型 |
|---|---|---|
| 雇员编号 | id | int |
| 雇员姓名 | name | varchar(30) |
| 雇员性别 | sex | enum |
| 雇用时期 | hire_date | date |
| 雇员职位 | post | varchar(50) |
| 职位描述 | job_description | varchar(100) |
| 雇员薪水 | salary | double(15,2) |
| 办公室 | office | int |
| 部门编号 | dep_id | int |
mysql> CREATE TABLE company.employee5(
id int primary key AUTO_INCREMENT not null,
name varchar(30) not null,
sex enum('male','female') default 'male' not null,
hire_date date not null,
post varchar(50) not null,
job_description varchar(100),
salary double(15,2) not null,
office int,
dep_id int
);
mysql> insert into company.employee5(name,sex,hire_date,post,job_description,salary,office,dep_id) values
('jack','male','20180202','instructor','teach',5000,501,100),
('tom','male','20180203','instructor','teach',5500,501,100),
('robin','male','20180202','instructor','teach',8000,501,100),
('alice','female','20180202','instructor','teach',7200,501,100),
('tianyun','male','20180202','hr','hrcc',600,502,101),
('harry','male','20180202','hr',NULL,6000,502,101),
('emma','female','20180206','sale','salecc',20000,503,102),
('christine','female','20180205','sale','salecc',2200,503,102),
('zhuzhu','male','20180205','sale',NULL,2200,503,102),
('gougou','male','20180205','sale','',2200,503,102);
mysql> SELECT 字段名称,字段名称2 from 表名 条件
mysql> SELECT column_name,column_2 from table WHERE ...
简单查询：
mysql> SELECT * from t3;
mysql> SELECT name, salary, dep_id from employee5;
避免重复DISTINCT
SELECT post FROM employee5;
SELECT DISTINCT post FROM employee5;
通过四则运算查询
运算：
mysql>SELECT 437.4384/5;
mysql>SELECT 5>3;
SELECT name, salary, salary*14 FROM employee5;
SELECT name, salary, salary*14 AS Annual_salary FROM employee5;
SELECT name, salary, salary*14 Annual_salary FROM employee5;
定义显示格式
CONCAT() 函数用于连接字符串
SELECT CONCAT(name, ' annual salary: ', salary*14) AS Annual_salary FROM employee5;
单条件查询
mysql> SELECT name from employee5 WHERE salary=5000;
多条件查询
mysql> SELECT name from employee5 WHERE salary>5000 and salary<6000;
关键字BETWEEN AND
SELECT name,salary FROM employee5 WHERE salary BETWEEN 5000 AND 15000;
SELECT name,salary FROM employee5 WHERE salary NOT BETWEEN 5000 AND 15000;
关键字IS NULL
SELECT name,job_description FROM employee5 WHERE job_description IS NULL;
SELECT name,job_description FROM employee5 WHERE job_description IS NOT NULL;
SELECT name,job_description FROM employee5 WHERE job_description='';
NULL说明：
1、等价于没有任何值、是未知数。
2、NULL与0、空字符串、空格都不同,NULL没有分配存储空间。
3、对空值做加、减、乘、除等运算操作，结果仍为空。
4、比较时使用关键字用“is null”和“is not null”。
5、排序时比其他数据都小，所以NULL值总是排在最前。
关键字IN集合查询
SELECT name, salary FROM employee5 WHERE salary=4000 OR salary=5000 OR salary=6000 OR salary=9000;
SELECT name, salary FROM employee5 WHERE salary IN (4000,5000,6000,9000) ;
SELECT name, salary FROM employee5 WHERE salary NOT IN (4000,5000,6000,9000) ;
排序查询
mysql> SELECT name from employee5 order by name;
mysql> SELECT name from employee5 order by name desc;
mysql> SELECT name from employee5 order by name desc limit 3; //限制次数
mysql> SELECT name from employee5 order by name desc limit 1,3;
mysql> SELECT name from employee5 order by name desc limit 2,3;
注：
ascending 美音 /?'s?nd??/ 升序
descending 美音 /d?'s?nd??/ 降序
按多列排序:
入职时间相同的人薪水不同
SELECT * FROM employee5 ORDER BY hire_date DESC,salary ASC;
有差别于
SELECT * from employee5 ORDER BY hire_date DESC;
先按入职时间，再按薪水排序
SELECT * from employee5 ORDER BY hire_date DESC,salary DESC;
先按职位，再按薪水排序
SELECT * from employee5 ORDER BY post,salary DESC;
限制查询的记录数
SELECT * FROM employee5 ORDER BY salary DESC LIMIT 5; //默认初始位置为0
SELECT * FROM employee5 ORDER BY salary DESC LIMIT 3,5; //从第4条开始，共显示5条
分组查询
GROUP BY和GROUP_CONCAT()函数一起使用
SELECT dep_id,GROUP_CONCAT(name) FROM employee5 GROUP BY dep_id;
SELECT dep_id,GROUP_CONCAT(name) as emp_members FROM employee5 GROUP BY dep_id;
模糊查询(通配符)
% 所有字符
mysql> SELECT * from employee5 WHERE salary like '%20%';
正则查询
SELECT * FROM employee5 WHERE salary REGEXP '72+'; 722222 7222222222
SELECT * FROM employee5 WHERE name REGEXP '^ali';
SELECT * FROM employee5 WHERE name REGEXP 'yun$';
SELECT * FROM employee5 WHERE name REGEXP 'm{1,8}';
函数
count()
max()
min()
avg()
database()
user()
now()
sum()
password()
SELECT COUNT(*) FROM employee5;
SELECT COUNT(*) FROM employee5 WHERE dep_id=101;
SELECT MAX(salary) FROM employee5;
SELECT MIN(salary) FROM employee5;
SELECT AVG(salary) FROM employee5;
SELECT SUM(salary) FROM employee5;
SELECT SUM(salary) FROM employee5 WHERE dep_id=101;
确保MySQL运行用户为一般用户
groupadd mysql
# useradd -M -s /sbin/nologin -g mysql mysql
# vim /etc/my.cnf
user = mysql
#注意点:
改变拥有者和所属组对于mysql的安装目录
建议修改默认端口3306,改为其他的一些端口
# vim /etc/my.cnf
port = 3306 false
port = 10086 true
开启mysql二进制日志,在误删除数据的情况下,可以通过二进制日志恢复到某个时间点
# vim /etc/my.cnf
log_bin = othername
4.删除空口令账号
#禁用匿名账号
# vim /etc/my.cnf
skip-grant-tables = 1. --改成 "#skip-grant-tables = 1"
#删除空口令用户
mysql> SELECT User,Host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| User | Host | authentication_string |
+---------------+-----------+-------------------------------------------+
| root | localhost | *AFE7E33F3C21EAE1BF8231C3B09F9B0184A670F6 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
+---------------+-----------+-------------------------------------------+
3 rows in set (0.00 sec)
mysql> create user 'newrain'@'localhost'; #(这是在做实验)创建空口令账户
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT User,Host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| User | Host | authentication_string |
+---------------+-----------+-------------------------------------------+
| root | localhost | *AFE7E33F3C21EAE1BF8231C3B09F9B0184A670F6 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| newrain | localhost | |
+---------------+-----------+-------------------------------------------+
4 rows in set (0.00 sec)
mysql> drop user 'newrain'@'localhost'; #这是删除空口令账户
Query OK, 0 rows affected (0.01 sec)
mysql> SELECT User,Host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| User | Host | authentication_string |
+---------------+-----------+-------------------------------------------+
| root | localhost | *AFE7E33F3C21EAE1BF8231C3B09F9B0184A670F6 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
+---------------+-----------+-------------------------------------------+
3 rows in set (0.00 sec)
禁止root账户远程访问(允许普通用户远程访问，某个网段即可)
mysql> SELECT User,Host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| User | Host | authentication_string |
+---------------+-----------+-------------------------------------------+
| root | localhost | *AFE7E33F3C21EAE1BF8231C3B09F9B0184A670F6 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
+---------------+-----------+-------------------------------------------+
3 rows in set (0.00 sec)
mysql> create user 'root'@'10.0.11.%' identified by "123";
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT User,Host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| User | Host | authentication_string |
+---------------+-----------+-------------------------------------------+
| root | localhost | *AFE7E33F3C21EAE1BF8231C3B09F9B0184A670F6 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| root | 10.0.11.% | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257 |
+---------------+-----------+-------------------------------------------+
4 rows in set (0.00 sec)
mysql> drop user 'root'@'10.0.11.%';
Query OK, 0 rows affected (0.00 sec)
使用mysql的时候,经常会遇到MySQL: ERROR 1040: Too many connections这样的问题,一种是访问量确实很高, MySQL服务器抗不住,这个时候就要考虑增加从服务器分散读压力,另外一种情况是MySQL配置文件中max_connections值过小, 这时就需要调整当前最大连接数
##设置最大连接数02
修改mysql配置文件my.cnf,在[mysqld]段中添加或修改max_connections值:
max_connections=256
DCL（Data Control Language 数据库控制语言）
用于数据库授权、角色控制等操作
GRANT 授权，为用户赋予访问权限
REVOKE 取消授权，撤回授权权限
登录和退出MySQL
远程登陆：
客户端语法：mysql -u用户名 -p密码 -hip地址 -P端口号:如果没有改端口号就不用-P指定端口
# mysql -h192.168.62.148 -P 3306 -uroot -p123
创建用户
create user '用户名'@'客户端来源IP地址' identified by '密码';
mysql> create user newrain@'192.168.62.%' identified by '123';
删除用户
drop user '用户名'@'客户端来源IP地址';
mysql> drop user newrain@'192.168.62.%';
修改用户
rename user '用户名'@'客户端来源IP地址' to '新用户名'@'客户端来源IP地址' ;
mysql> rename user newrain@'192.168.62.%' to ehome@'%';
修改密码
// 第一种方法：
set password for '用户名'@'IP地址'=Password('新密码')
mysql> set password for ehome@'%'=Password('123');
// 第二种方法：
alter user '用户名'@'客户端来源IP地址' identified by '新密码';
// 第三种方法(忘记密码时，必须使用此方法修改密码)：
UPDATE mysql.user SET authentication_string=password('QFedu123!') WHERE user='root' and host='localhost';
＝＝＝root修改自己密码
# mysqladmin -uroot -p'123' password 'new_password' //123为旧密码
案例:
# mysqladmin -uroot -p'123' password 'qf@123';
PS：用户权限相关数据保存在mysql数据库的user表中，所以也可以直接对其进行操作（不建议）
grant 权限 on 数据库.表 to '用户'@'客户端来源IP地址' identified by '密码'; -- 授权并设置密码
revoke 权限 on 数据库.表 from '用户'@'客户端来源IP地址' -- 取消权限
grant select on Company.employee to 'ehome'@'%' identified by 'Qianfeng@123'
revoke select on Company.employee from 'ehome'@'%'
mysql> grant all privileges on company.* to ehome@'%';
mysql> revoke all privileges on company.* from ehome@'%';
mysql> flush privileges; #关于权限方面的修改，注意刷新权限，否则有可能不生效
查看授权语句
show grants for '用户'@'客户端来源IP地址';
mysql> show grants for ehome@'%';
+-----------------------------------+
| Grants for ehome@% |
+-----------------------------------+
| GRANT USAGE ON *.* TO 'ehome'@'%' |
+-----------------------------------+
1 row in set (0.00 sec
查看生效的授权信息
针对所有库和表的权限，比如 *.* 。 去 mysql.user 中查看
SELECT * from mysql.user WHERE user='root'\G
mysql> SELECT * from mysql.user WHERE user='ehome'\G
*************************** 1. row ***************************
Host: %
User: ehome
SELECT_priv: N
Insert_priv: N
Update_priv: N
Delete_priv: N
Create_priv: N
Drop_priv: N
Reload_priv: N
Shutdown_priv: N
Process_priv: N
File_priv: N
Grant_priv: N
References_priv: N
Index_priv: N
Alter_priv: N
Show_db_priv: N
Super_priv: N
Create_tmp_table_priv: N
Lock_tables_priv: N
Execute_priv: N
Repl_slave_priv: N
Repl_client_priv: N
Create_view_priv: N
Show_view_priv: N
Create_routine_priv: N
Alter_routine_priv: N
Create_user_priv: N
Event_priv: N
Trigger_priv: N
Create_tablespace_priv: N
ssl_type:
ssl_cipher:
x509_issuer:
x509_subject:
max_questions: 0
max_updates: 0
max_connections: 0
max_user_connections: 0
plugin: mysql_native_password
authentication_string: *23AE809DDACAF96AF0FD78ED04B6A265E05AA257
password_expired: N
password_last_changed: 2019-08-20 19:35:41
password_lifetime: NULL
account_locked: N
1 row in set (0.00 sec)
针对具体到库的权限，比如db_name.* 。 去 mysql.db 中查看
mysql> SELECT * from mysql.db WHERE user='ehome'\G
*************************** 1. row ***************************
Host: %
Db: company
User: ehome
SELECT_priv: Y
Insert_priv: Y
Update_priv: Y
Delete_priv: Y
Create_priv: Y
Drop_priv: Y
Grant_priv: N
References_priv: Y
Index_priv: Y
Alter_priv: Y
Create_tmp_table_priv: Y
Lock_tables_priv: Y
Create_view_priv: Y
Show_view_priv: Y
Create_routine_priv: Y
Alter_routine_priv: Y
Execute_priv: Y
Event_priv: Y
Trigger_priv: Y
1 row in set (0.00 sec)
假如是 MySQL8.x
CREATE USER '你的用户名'@'localhost' IDENTIFIED BY '你的密码';
#创建新的用户
GRANT ALL PRIVILEGES ON 你的数据库名.* TO '你的用户名'@'localhost';
#把刚刚创建的数据库的管理权限给予刚刚创建的MySQL用户
FLUSH PRIVILEGES;
#刷新权限，使用设置生效