Mysql学习

Mysql常用语句

第一招、mysql服务的启动和停止
net stop mysql
net start mysql
第二招、登陆mysql
语法如下： mysql -u用户名 -p用户密码
键入命令mysql -uroot -p， 回车后提示你输入密码，输入12345，然后回车即可进入到mysql中了，mysql的提示符是：
mysql>
注意，如果是连接到另外的机器上，则需要加入一个参数-h机器IP
第三招、增加新用户
格式：grant 权限 on 数据库.* to 用户名@登录主机 identified by "密码"
如，增加一个用户user1密码为password1，让其可以在本机上登录， 并对所有数据库有查询、插入、修改、删除的权限。首先用以root用户连入mysql，然后键入以下命令：
grant select,insert,update,delete on *.* to user1@localhost Identified by "password1";
如果希望该用户能够在任何机器上登陆mysql，则将localhost改为"%"。
如果你不想user1有密码，可以再打一个命令将密码去掉。
grant select,insert,update,delete on mydb.* to user1@localhost identified by "";
第四招： 操作数据库
登录到mysql中，然后在mysql的提示符下运行下列命令，每个命令以分号结束。
1、 显示数据库列表。
show databases;
缺省有两个数据库：mysql和test。 mysql库存放着mysql的系统和用户权限信息，我们改密码和新增用户，实际上就是对这个库进行操作。
2、 显示库中的数据表：
use 库名;
show tables;
3、 显示数据表的结构：
describe 表名; desc 表名;
4、 建库与删库：
create database 库名;
drop database 库名;
5、 建表与删表：
use 库名;
create table 表名(字段列表); 例如：CREATE TABLE user (name VARCHAR(20), sex CHAR(1));
drop table 表名;
6、 清空表中记录：
delete from 表名 where ... ;   没有where会删除所用的记录。
7、 显示表中的记录：
select * from 表名;

8、往表中加入记录
insert into user values ("hyq","M"); 此法必须列出所有字段的值。（按顺序）
insert into user (name, sex) values ("hyq","M");

9、更新表中数据
update user set sex="f" where name='hyq';

10、修改表名
ALTER TABLE 表名 RENAME [TO|AS] 新表名
ALTER TABLE user10 RENAME TO user11;     或
RENAME TABLE 表名 TO 新表名； 这里面的TO不可以省略

11、修改字段（字段就是列名）
修改字段类型
alter table 表名 modify column 字段 varchar(25);
修改字段名
alter table 表名 change 字段名 新字段名 类型 ; //一定要带类型，因为原来字段的所有属性清空了。
alter table tablename change id id int auto_increment primary key;
增加字段
alter table 表名 add 字段名 类型;
删除字段
alter table 表名 drop 字段名;
删除主键
alter table 表名 drop primary key; //这是该字段没有设置auto_increment 的时候，可以用。
alter table 表名 modify id int, drop primary key; //当字段id设置了auto_increment 时，删除主键

第五招、导出和导入数据
1. 导出数据：
mysqldump --opt test > mysql.test
即将数据库test数据库导出到mysql.test文件，后者是一个文本文件
如：mysqldump -u root -p123456 --databases dbname > mysql.dbname
就是把数据库dbname导出到文件mysql.dbname中。
如：mysqldump -uroot -p123456 数据库名 表名 > test.sql (即文件名，路径是当前路径)

2. 导入数据:
mysqlimport -u root -p123456 < mysql.dbname。
不用解释了吧。
3. 将文本数据导入数据库:
文本数据的字段数据之间用tab键隔开。
use test;
load data local infile "文件名" into table 表名;

4.导入.sql文件命令(例如D:/mysql.sql)
mysql>use database;
mysql>source d:/mysql.sql;

5、退出MYSQL命令：quit / exit (回车) 
====================================
DML 数据操作语言
对表记录的增删改
插入：INSERT INTO 表名（列1，列2，...） VALUES(值1，值2，...)
SELECT * FROM 表名；——显示
更新：UPDATE 表名 SET 列1=列值1，列2=列值2，WHERE 条件；
             注意，不加where会修改列的所有值。
删除：DELETE FROM 表名 WHERE 条件
             注意：不加where会删除表的所有记录。
另外，delete后，再添加，id会不连续。
还有一个删除表记录的是：TRUNCAT 表名 是DDL的

DCL数据控制语言
修改密码：
法1：mysqladmin -uroot -p旧密码 password 新密码
法2：update mysql.user set password=PASSWORD('新密码') where user='root';
若忘记了密码，则
关闭数据库
mysqld --skip-grant-tables
然后
mysql
进入修改密码

创建用户
CREATE USER 用户名 @'IP地址' IDENTIFIED BY '密码'
此用户只能在指定的ip上使用，所有的IP要使用%

用户授权
GRANT 权限1，权限2,... ON 数据库名.* TO 用户名 @IP地址
例如：grant select，update，insert on shop.* to ‘test1’ @‘196.168.1.106’

撤销权限
REVOKE 权限1，... ON 数据库名.* FROM 用户名 @ip地址

用户创建与授权一句：
grant 权限1，... on 数据库名.* to 用户名@ip地址 identified by 密码
flush privileges

显示权限
show grant for 'test'@'192.16.8.1.0';
删除用户
DROP USER 用户名@IP地址
=====================================================================

---

 

事务：一个sql语句就是一个事务，事务可以保证一组sql语句要么都成功要么都失败。

1. 可以关闭 set autocommit=0关闭自动提交，最后插入或修改时 只有commit才会最终存入。

2. 语句格式如下

start transaction; # start transaction 表示开启一个事务，或者用 begin 或 begin work
sql语句。。。
如果上面的sql语句没有问题
commit（提交）-》写入磁盘
如果有问题
rollback（回滚）-》不写入磁盘

原子性：一个事务中的所有语句，要么全做，要么全不做。

一致性：让数据保持逻辑上的“合理性”，比如，一个商品出库时，既要仓库中的数目减1，又要让用户的商品数加1 。

隔离性：如果多个事务同时并发执行，但每一个事务就像各自执行一样。

持久性：一个事务执行成功，则对数据来说应该是一个明确的硬盘数据更改，而不仅仅是内存中的变化。

 

---

触发器

1、创建触发器

　　create trigger 触发器名 after / before   insert / update / delete    on 表名  for each row
　　begin
　　　　sql语句
　　end;

2、查看触发器

　　show create trigger 触发器名

3、删除触发器

　　drop trigger 触发器名

---

  查询sql语句的执行时间的方法：

　　show variables like '%profiling%'
　　set profiling = on
　　show profile for query 2

建议：在where后的条件加索引。速度快。
使用 like 模糊时，右模糊（若有索引会用索引）快，左模糊和全模糊（不会用索引）慢。例如：右模糊 like 'wang%'  左模糊 like '%wang'   全模糊 like '%wang%'

explain select * from user where pid = 123 or password = ‘555’       查看具体语句的执行

---

• Mysql 三种连接

连接就是从两个表的笛卡尔积运算结果中选取某些行和列。换句话说，连接就是有条件的笛卡尔积。笛卡尔积关系运算：看这 www.cnblogs.com/htj10/p/10825360.html 的最后一项。

• INNER JOIN（内连接,或等值连接）：获取两个表中字段匹配关系的记录。
• LEFT JOIN（左连接）：获取左表所有记录，即使右表没有对应匹配的记录。
• RIGHT JOIN（右连接）： 与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录。

栗子：表stu1，表stu2

mysql> select * from stu1;
+----------+---------+------+------+
| id       | name    | sex  | age  |
+----------+---------+------+------+
| 12720510 | ljq     | M    |   26 |
| 12720511 | ljl     | M    |   25 |
| 12720512 | yangKai | M    |   26 |
+----------+---------+------+------+
mysql> select * from stu2;
+----------+-------------+-------+
| id       | course      | score |
+----------+-------------+-------+
| 12720510 | Chemistry   |    65 |
| 12720512 | Mathematics |    75 |
| 12720515 | C++         |    87 |
+----------+-------------+-------+

select * from stu1,stu2; ---> 这就是笛卡尔积，like  (a+b+c)*(d+e) = a*d + b*d + c*d + a*e + b*e + c*e

mysql> select * from stu1,stu2;
+----------+---------+------+------+----------+-------------+-------+
| id       | name    | sex  | age  | id       | course      | score |
+----------+---------+------+------+----------+-------------+-------+
| 12720510 | ljq     | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720511 | ljl     | M    |   25 | 12720510 | Chemistry   |    65 |
| 12720512 | yangKai | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720510 | ljq     | M    |   26 | 12720512 | Mathematics |    75 |
| 12720511 | ljl     | M    |   25 | 12720512 | Mathematics |    75 |
| 12720512 | yangKai | M    |   26 | 12720512 | Mathematics |    75 |
| 12720510 | ljq     | M    |   26 | 12720515 | C++         |    87 |
| 12720511 | ljl     | M    |   25 | 12720515 | C++         |    87 |
| 12720512 | yangKai | M    |   26 | 12720515 | C++         |    87 |
+----------+---------+------+------+----------+-------------+-------+

加上where条件后，select * from stu1,stu2 where stu1.id = stu2.id;

mysql> select * from stu1,stu2 where stu1.id = stu2.id;
+----------+---------+------+------+----------+-------------+-------+
| id       | name    | sex  | age  | id       | course      | score |
+----------+---------+------+------+----------+-------------+-------+
| 12720510 | ljq     | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720512 | yangKai | M    |   26 | 12720512 | Mathematics |    75 |
+----------+---------+------+------+----------+-------------+-------+

select stu1.id, name, course, score from stu1.id = stu2.id;  选择部分列（相同列名的要加表名限制，像stu1.id）

mysql> select stu1.id, name, course, score from stu1,stu2 where stu1.id = stu2.id;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720510 | ljq     | Chemistry   |    65 |
| 12720512 | yangKai | Mathematics |    75 |
+----------+---------+-------------+-------+
2 rows in set (0.00 sec)

• inner join

select * from stu1 inner join stu2;（可省略inner）  与  select * from stu1,stu2; 一样，都是笛卡尔积。 

mysql> select * from stu1 inner join stu2; 
+----------+---------+------+------+----------+-------------+-------+
| id       | name    | sex  | age  | id       | course      | score |
+----------+---------+------+------+----------+-------------+-------+
| 12720510 | ljq     | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720511 | ljl     | M    |   25 | 12720510 | Chemistry   |    65 |
| 12720512 | yangKai | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720510 | ljq     | M    |   26 | 12720512 | Mathematics |    75 |
| 12720511 | ljl     | M    |   25 | 12720512 | Mathematics |    75 |
| 12720512 | yangKai | M    |   26 | 12720512 | Mathematics |    75 |
| 12720510 | ljq     | M    |   26 | 12720515 | C++         |    87 |
| 12720511 | ljl     | M    |   25 | 12720515 | C++         |    87 |
| 12720512 | yangKai | M    |   26 | 12720515 | C++         |    87 |
+----------+---------+------+------+----------+-------------+-------+
9 rows in set (0.00 sec)

 用 on 加条件，用 where 加条件。注：where后面增加的条件是对临时表生成后，进行过滤的。而on条件是在生成临时表时使用的条件。

mysql> select stu1.id, name, course, score, age from stu1 inner join stu2 on stu1.id = stu2.id;
+----------+---------+-------------+-------+------+
| id       | name    | course      | score | age  |
+----------+---------+-------------+-------+------+
| 12720510 | ljq     | Chemistry   |    65 |   26 |
| 12720512 | yangKai | Mathematics |    75 |   26 |
+----------+---------+-------------+-------+------+
2 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score, age from stu1 inner join stu2 where stu1.id = stu2.id;
+----------+---------+-------------+-------+------+
| id       | name    | course      | score | age  |
+----------+---------+-------------+-------+------+
| 12720510 | ljq     | Chemistry   |    65 |   26 |
| 12720512 | yangKai | Mathematics |    75 |   26 |
+----------+---------+-------------+-------+------+
2 rows in set (0.00 sec)

• left join

注意：left / right join 后不能不加on条件。可以这么写 select * from stu1 left join stu2 on 1=1；这样也是笛卡尔积。

mysql> select * from stu1 left join stu2;
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> select * from stu1 left join stu2 on stu1.id = stu2.id;
+----------+---------+------+------+----------+-------------+-------+
| id       | name    | sex  | age  | id       | course      | score |
+----------+---------+------+------+----------+-------------+-------+
| 12720510 | ljq     | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720512 | yangKai | M    |   26 | 12720512 | Mathematics |    75 |
| 12720511 | ljl     | M    |   25 |     NULL | NULL        |  NULL |
+----------+---------+------+------+----------+-------------+-------+
3 rows in set (0.00 sec)

　　where 是在表连接之后在进行过滤的。on 是表连接时的条件。

mysql> select stu1.id, name, course, score from stu1 left join stu2 on stu1.id = stu2.id;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720510 | ljq     | Chemistry   |    65 |
| 12720512 | yangKai | Mathematics |    75 |
| 12720511 | ljl     | NULL        |  NULL |
+----------+---------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 left join stu2 on stu1.id = stu2.id and stu1.id=12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720512 | yangKai | Mathematics |    75 |
| 12720510 | ljq     | NULL        |  NULL |
| 12720511 | ljl     | NULL        |  NULL |
+----------+---------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 left join stu2 on stu1.id = stu2.id where stu1.id=12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720512 | yangKai | Mathematics |    75 |
+----------+---------+-------------+-------+
1 row in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 left join stu2 on stu1.id = stu2.id and stu2.id=12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720510 | ljq     | NULL        |  NULL |
| 12720511 | ljl     | NULL        |  NULL |
| 12720512 | yangKai | Mathematics |    75 |
+----------+---------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 left join stu2 on stu1.id = stu2.id where stu2.id=12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720512 | yangKai | Mathematics |    75 |
+----------+---------+-------------+-------+
1 row in set (0.00 sec)

• right join

mysql> select * from stu1 right join stu2 on stu1.id = stu2.id;
+----------+---------+------+------+----------+-------------+-------+
| id       | name    | sex  | age  | id       | course      | score |
+----------+---------+------+------+----------+-------------+-------+
| 12720510 | ljq     | M    |   26 | 12720510 | Chemistry   |    65 |
| 12720512 | yangKai | M    |   26 | 12720512 | Mathematics |    75 |
|     NULL | NULL    | NULL | NULL | 12720515 | C++         |    87 |
+----------+---------+------+------+----------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 right join stu2 on stu1.id = stu2.id;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720510 | ljq     | Chemistry   |    65 |
| 12720512 | yangKai | Mathematics |    75 |
|     NULL | NULL    | C++         |    87 |
+----------+---------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 right join stu2 on stu1.id = stu2.id and stu1.id = 12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
|     NULL | NULL    | Chemistry   |    65 |
| 12720512 | yangKai | Mathematics |    75 |
|     NULL | NULL    | C++         |    87 |
+----------+---------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 right join stu2 on stu1.id = stu2.id where stu1.id = 12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720512 | yangKai | Mathematics |    75 |
+----------+---------+-------------+-------+
1 row in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 right join stu2 on stu1.id = stu2.id and stu2.id = 12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720512 | yangKai | Mathematics |    75 |
|     NULL | NULL    | Chemistry   |    65 |
|     NULL | NULL    | C++         |    87 |
+----------+---------+-------------+-------+
3 rows in set (0.00 sec)

mysql> select stu1.id, name, course, score from stu1 right join stu2 on stu1.id = stu2.id where stu2.id = 12720512;
+----------+---------+-------------+-------+
| id       | name    | course      | score |
+----------+---------+-------------+-------+
| 12720512 | yangKai | Mathematics |    75 |
+----------+---------+-------------+-------+
1 row in set (0.00 sec)

 

---

•  group by 

mysql> select * from stu2;
+----------+-------------+-------+
| id       | course      | score |
+----------+-------------+-------+
| 12720515 | C++         |    87 |
| 12720510 | Chemistry   |    65 |
| 12720512 | Mathematics |    75 |
| 12720510 | C++         |    89 |
| 12720512 | Chemistry   |    85 |
+----------+-------------+-------+
5 rows in set (0.00 sec)
//group by id     以id为分组的依据
//order by sum(score) asc;  以id为分组的分数之和排序（asc升序 desc降序，默认是升序）
mysql> select id as xuehao, sum(score) as zongfen from stu2 group by id order by sum(score) asc;
+----------+---------+
| xuehao   | zongfen |
+----------+---------+
| 12720515 |      87 |
| 12720510 |     154 |
| 12720512 |     160 |
+----------+---------+
3 rows in set (0.09 sec)
 
mysql> select id as xuehao, avg(score) as average from stu2 group by id order by avg(score) desc;
+----------+---------+
| xuehao   | average |
+----------+---------+
| 12720515 | 87.0000 |
| 12720512 | 80.0000 |
| 12720510 | 77.0000 |
+----------+---------+
3 rows in set (0.00 sec)

mysql> select course as kemu, count(*) as renshu from stu2 group by course;
+-------------+--------+
| kemu        | renshu |
+-------------+--------+
| C++         |      2 |
| Chemistry   |      2 |
| Mathematics |      1 |
+-------------+--------+
3 rows in set (0.00 sec)

　　

 标准偏差：

1. 总体标准偏差 $$ \sigma = \sqrt{\frac{1}{N}\sum_{i=1}^{N}(x_i-\overline{x})^2} $$

2. 样本标准偏差 $$ \sigma = \sqrt{\frac{1}{N-1}\sum_{i=1}^{N}(x_i-\overline{x})^2} $$

mysql 求总体标准偏差：STD(expression) , STDDEV(expression), STDDEV_POP(expression)，总体标准差的平方：VAR_POP(expression)，VARIANCE(expression)

mysql 求样本标准偏差：STDDEV_SAMP(expression)，样本标准差的平方：VAR_SAMP(expression)

 STDDEV(expression)计算当前行关于组的标准偏离
 STDDEV_POP(expression)该函数计算总体标准偏离，并返回总体变量的平方根，其返回值与 VAR_POP 函数的平方根相同
 STDDEV_SAMP(expression)该函数计算累积样本标准偏离，并返回样本变量的平方根，其返回值与 VAR_SAMP 函数的平方根相同

mysql> select course as kemu, stddev(score) as STDEV, stddev_samp(score) as STDEVP from stu2 group by course;
+-------------+-------+--------------------+
| kemu        | STDEV | STDEVP             |
+-------------+-------+--------------------+
| C++         |     1 | 1.4142135623730951 |
| Chemistry   |    10 | 14.142135623730951 |
| Mathematics |     0 |               NULL |
+-------------+-------+--------------------+
3 rows in set (0.00 sec)
//或者
mysql> select course as kemu, std(score) as STDEV, stddev_samp(score) as STDEVP from stu2 group by course;
+-------------+-------+--------------------+
| kemu        | STDEV | STDEVP             |
+-------------+-------+--------------------+
| C++         |     1 | 1.4142135623730951 |
| Chemistry   |    10 | 14.142135623730951 |
| Mathematics |     0 |               NULL |
+-------------+-------+--------------------+
3 rows in set (0.00 sec)

　　

mysql> select * from stu2;
+----------+-------------+-------+
| id       | course      | score |
+----------+-------------+-------+
| 12720515 | C++         |    87 |
| 12720510 | Chemistry   |    65 |
| 12720512 | Mathematics |    75 |
| 12720510 | C++         |    89 |
| 12720512 | Chemistry   |    85 |
+----------+-------------+-------+
5 rows in set (0.00 sec)

mysql> select course as kemu, max(score) as MAX, min(score) as MIN from stu2 group by course;
+-------------+------+------+
| kemu        | MAX  | MIN  |
+-------------+------+------+
| C++         |   89 |   87 |
| Chemistry   |   85 |   65 |
| Mathematics |   75 |   75 |
+-------------+------+------+
3 rows in set (0.04 sec)

　　

 

转载于:https://www.cnblogs.com/htj10/p/10164376.html