Mysql数据库基础笔记
一、前言
- mysql和linux php,apache配合紧密，LAMP架构
- mysql开源免费
- 默认端口3306
- set name gbk
二、安装启动服务
mysqld -install
net start mysql
mysql -uroot -proot
三、修改用户密码
mysql> set password for root@localhost=password('root'); //加密码
mysql> select user,password from mysql.user; //查看密码
mysql> use mysql;
mysql> update user set password=password('123') where user='root'; //改密码
mysql> flush privileges; //刷新权限
忘记root密码
- 关闭正在运行的MySQL服务
- 管理员运行DOS窗口，转到mysql\bin目录
- mysqld --skip-grant-tables //启动MySQL服务的时候跳过权限表认证
- 再开一个DOS窗口(因为刚才那个DOS窗口已经不能动了)，输入mysql回车
- 修改密码
- 重启服务
四、基本语句
1.库操作
mysql> show databases; //查库
mysql> use mysql; //选库
mysql> create database db1 charset utf8; //创建库
mysql> drop database db1; //删除数据库
//mysql中数据库不能改名，表/列可以改名
2.表操作
mysql> show tables; //查表
+---------------+
| Tables_in_db1 |
+---------------+
| class |
| student |
+---------------+
mysql> create table student( //创建表
-> Snum int,
-> Sname varchar(10),
-> Ssex char(2)
-> )engine myisam charset utf8;
mysql> drop table student; //删除表
mysql> rename table student to stu; //重命表名
mysql> insert into stu values //插入数据
-> (1,'张三'),
-> (2,'lisi'),
-> (3,'王五');
mysql> select * from stu; //查数据
mysql> truncate stu; //清空表数据
mysql> insert into student values
-> \c //退出本语句
mysql> create table class( //创建表
-> id int primary key auto_increment,
-> sname varchar(10) not null default '',
-> sex char(1) not null default '',
-> company varchar(20) default 'null',
-> salary decimal(6,2) default 0.00,
-> other varchar(20) default '无'
-> )engine myisam charset utf8;
mysql> desc class; //查看表结构
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| sname | varchar(10) | NO | | | |
| sex | char(1) | NO | | | |
| company | varchar(20) | YES | | null | |
| salary | decimal(6,2) | YES | | 0.00 | |
| other | varchar(20) | YES | | 无 | |
+---------+--------------+------+-----+---------+----------------+
mysql> alter table class add score tinyint unsigned not null default 0; //增加一个score列
mysql> alter table student add money float(7,2) default 0;
五、数据操作
1、增——Insert
mysql> insert into class
-> (id,sname,sex,company,salary,other) values (1,'张三','女','','10000.00','工作地址在广州');
mysql> insert into class
-> (sname,sex,salary) values ('李四','女','9000');
mysql> insert into class (sname) values ('王五');
mysql> insert into class (sname) values ('王五'),('赵六'),('顾七');
mysql> insert into class values
-> (7,'吴八','男','百度',8734.32,'深圳任职');
mysql> select * from class;
+----+-------+-----+---------+---------+----------------+
| id | sname | sex | company | salary | other |
+----+-------+-----+---------+---------+----------------+
| 1 | 张三 | 女 | | 9999.99 | 工作地址在广州 |
| 2 | 李四 | 女 | null | 9000.00 | 无 |
| 3 | 王五 | | null | 0.00 | 无 |
| 4 | 王五 | | null | 0.00 | 无 |
| 5 | 赵六 | | null | 0.00 | 无 |
| 6 | 顾七 | | null | 0.00 | 无 |
| 7 | 吴八 | 男 | 百度 | 8734.32 | 深圳任职 |
+----+-------+-----+---------+---------+----------------+
mysql> insert into db1.goods select goods_id,cat_id,goods_name from gyshop.goods; //从其他库导入插入数据，要求导入所有列
2、改——Update
- update 表名 set 列1=’ ‘，列2=’ ’ where expr;
mysql> update class set sex='男',company='皇家亲戚' where sname='王五';
mysql> update class set salary = 5000 where salary =0.00;
mysql> update class set other = '目前离职状态' where salary <=9000 and sex = '';
mysql> select * from class;
+----+-------+-----+----------+---------+----------------+
| id | sname | sex | company | salary | other |
+----+-------+-----+----------+---------+----------------+
| 1 | 张三 | 女 | 千度 | 9999.99 | 工作地址在广州 |
| 2 | 李四 | 女 | 千度 | 9000.00 | 无 |
| 3 | 王五 | 男 | 皇家亲戚 | 5000.00 | 无 |
| 4 | 王五 | 男 | 皇家亲戚 | 5000.00 | 无 |
| 5 | 赵六 | | 千度 | 5000.00 | 目前离职状态 |
| 6 | 顾七 | | 千度 | 5000.00 | 目前离职状态 |
| 7 | 吴八 | 男 | 百度 | 8734.32 | 深圳任职 |
+----+-------+-----+----------+---------+----------------+
3、删——Delete
- delete from 表名 where expr;
mysql> delete from class where sname ='王五' or company='百度';
mysql> select * from class;
+----+-------+-----+---------+---------+----------------+
| id | sname | sex | company | salary | other |
+----+-------+-----+---------+---------+----------------+
| 1 | 张三 | 女 | 千度 | 9999.99 | 工作地址在广州 |
| 2 | 李四 | 女 | 千度 | 9000.00 | 无 |
| 5 | 赵六 | | 千度 | 5000.00 | 目前离职状态 |
| 6 | 顾七 | | 千度 | 5000.00 | 目前离职状态 |
+----+-------+-----+---------+---------+----------------+
mysql> delete from class; //直接删除所有表数据
mysql> select * from class;
Empty set (0.00 sec)
mysql> truncate stu; //清空表数据
4、查——Select
- select 列1，列2，列n from 表名 where expr；
mysql> select * from class; //查表所有数据
+----+-------+-----+---------+--------+-------+
| id | sname | sex | company | salary | other |
+----+-------+-----+---------+--------+-------+
| 8 | 张三 | 男 | null | 0.00 | 无 |
| 9 | 李四 | 女 | null | 0.00 | 无 |
| 10 | 王五 | 女 | null | 0.00 | 无 |
+----+-------+-----+---------+--------+-------+
mysql> select sname from class where sex='女'; //查询指定列数据
+-------+
| sname |
+-------+
| 李四 |
| 王五 |
+-------+
1. where条件查询
where是针对原表的一个表达式布尔判断
mysql> select goods_id,goods_name from goods where goods_id = 2;
mysql> select goods_id,goods_name from goods where goods_id != 2;
mysql> select goods_id,goods_name from goods where goods_id <> 2;
mysql> select goods_id,goods_name from goods where shop_price > 2000;
mysql> select goods_id,goods_name from goods where shop_price >= 4;
mysql> select goods_id,goods_name from goods where goods_id in (1,4);
mysql> select goods_id,goods_name from goods where goods_id between 2 and 4;
mysql> select goods_id,goods_name from goods where goods_name like '平板%';
mysql> select goods_id,goods_name from goods where goods_name like '%平板%';
mysql> select goods_id,goods_name from goods where goods_name like '__平板';
mysql> select goods_id,goods_name from goods where goods_name like '手机K_';
mysql> select goods_id,goods_name from goods where goods_id != 2 and goods_id !=3;
mysql> select goods_id,goods_name from goods where goods_id not in (2,3);
mysql> select goods_id,goods_name from goods where goods_name not like '平板%';
mysql> select goods_id,goods_name from goods where goods_id > 1 and goods_id < 3 or goods_id > 4 and goods_id < 7;
mysql> select goods_id,goods_name from goods where shop_price >= 4 and goods_id > 4 and goods_id < 7;
mysql> select goods_id,goods_name from goods where shop_price = 0 and (goods_id < 4 or goods_id > 7 and goods_id <= 9) and goods_name like '%平板%';
mysql> select goods_name,market_price-shop_price from goods where 1;
mysql> select goods_name,(market_price-shop_price) as discount from goods where 1;
mysql> select goods_name,(market_price-shop_price) as discount from goods where (market_price-shop_price) > 1000;
2.group by分组查询
- 五个聚合函数：sum,avg,max,min,count,group
mysql> select max(market_price) from goods;
mysql> select min(market_price) as MIN from goods;
mysql> select sum(goods_number) from goods;
mysql> select sum(goods_number) from goods where cat_id=3;
mysql> select avg(shop_price) from goods;
mysql> select count(*) from goods;
mysql> select cat_id,count(*),sum(market_price) from goods group by cat_id;
- 严格的讲，以group by a,b,c为列，则select的列只能在a,b,c里选择，语义上才没有矛盾；
3.having 筛选
mysql> select goods_name,(market_price-shop_price) as discount from goods where (market_price-shop_price)>=500;
+----------------+----------+
| goods_name | discount |
+----------------+----------+
| 手机 | 1100.00 |
| 平板屏幕总成 | 500.00 |
| 平板屏幕单机版 | 500.00 |
+----------------+----------+
mysql> select goods_name,(market_price-shop_price) as discount from goods having discount >= 500;
+----------------+----------+
| goods_name | discount |
+----------------+----------+
| 手机 | 1100.00 |
| 平板屏幕总成 | 500.00 |
| 平板屏幕单机版 | 500.00 |
+----------------+----------+
mysql> select cat_id,sum(market_price) as discount from goods group by cat_id having discount >5000;
+--------+----------+
| cat_id | discount |
+--------+----------+
| 2 | 6000.00 |
| 3 | 7997.00 |
+--------+----------+
mysql> select name,avg(score),sum(score<60) as gk from result group by name having gk>=2;
4.order by 排序
5、limit 限制结果条数
六、表操作
1、增——Create
mysql> create table db1.member( //建表
-> id int unsigned auto_increment primary key,
-> username char(20) not null default '',
-> gender char(1) not null default '',
-> weight tinyint unsigned not null default 0,
-> birth date not null default 0,
-> salary decimal(8,2) not null default 0,
-> lastlogin timestamp not null default 0
-> )engine myisam charset utf8;
mysql> show create table member; //查看建表语句
+--------+------------------------------------------------------------------------------+
| Table | Create Table |
+--------+------------------------------------------------------------------------------+
| member | CREATE TABLE `member` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`username` char(20) NOT NULL DEFAULT '',
`gender` char(1) NOT NULL DEFAULT '',
`weight` tinyint(3) unsigned NOT NULL DEFAULT '0',
`birth` date NOT NULL DEFAULT '0000-00-00',
`salary` decimal(8,2) NOT NULL DEFAULT '0.00',
`lastlogin` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------+------------------------------------------------------------------------------+
2、改——Alter
mysql> alter table student add age tinyint not null default 0; //默认加的列在表最后
mysql> alter table test add gender char(1) not null default 0 after star;
//把新列加在某列后
mysql> alter table test add id int unsigned not null auto_increment primary key first; //把新列加载最前面
mysql> alter table test drop gender; //删除列
mysql> alter table test modify gender char(4) not null default ''; //修改列类型
mysql> alter table test change gender sex char(2); //修改列名和列类型
3、删——Drop
mysql> drop table student;
4、查——Show
mysql> show tables; //查表名
mysql> desc student; //查表结构
九、其他
1.保存操作记录
mysql> tee C:\Users\LQN\Desktop\Temp\0525.sql
Logging to file 'C:\Users\LQN\Desktop\Temp\0525.sql'
mysql> #把敲的sql及结果都输出到一个sql文件里
mysql> #便于溯源
2.数据类型
整型：
| 类型 | 大小 | 参数 | 范围 |
|---|---|---|---|
| tinyint | 1 | unsigned/zerofill | 0-255/-128-127 |
| smallint | 2 | unsigned/zerofill | 0-65535/-32768-32767 |
| mediumint | 3 | unsigned/zerofill | |
| int | 4 | unsigned/zerofill | |
| bigint | 8 | unsigned/zerofill |
浮点型：
| 类型 | 大小 | 描述 |
|---|---|---|
| float(M,D) | 4/8 | M叫“精度”，代表“总位数” |
| decimal(M,D) | D是“标度”，代表“小数位” |
mysql> alter table student add money float(7,2) default 0;
字符串型：
| 类型 | 描述 | 长度 | |
|---|---|---|---|
| char | 定长类型 | 尾部空格补够长度 | 0-255 |
| varchar | 变长类型 | 有1-2个字节来标志该列的内容长度 | 0-65535 |
| text | 文本类型 | 搜索速度慢 | |
| blob | 二进制类型 | 存储图像和音频等二进制信息 |
日期/时间类型：
| 类型 | 说明 | 标准格式 | 范围 |
|---|---|---|---|
| date | 日期 | YYYY-MM-DD | 1000-01-01到9999-12-31 |
| time | 时间 | HH:MM:SS | |
| datetime | 日期时间 | YYYY-MM-DD HH:MM:SS | |
| year | 年份类型 | YYYY | 1901-2155 |
| timestamp | 时间戳 | 默认插入数据的 当前时间 |
十、SQL优化
1）基本写法优化
- 少使用select * ,尽量使用具体字段；
- 对于条件来说等号之类两边的字段类型要一致，字符串不加单引号索引会失效；
- 尽量少使用Order by 排序，对于需要多个字段进行排序的可以使用组合索引；
- 对于groud by语句要先过滤后分组；
- 在查询时减少使用null，对字段有多个null的可以加默认值；
- 少使用like，对于需要使用的，如需要使用尽量用like abc%这种，不要把%放字段前面；
- 在where后面少使用函数或者算数运算；
- 去除的distinct过滤字段要少，避免distinct *；
- 不要超过5个以上的表连接。
2）建立使用合适索引
- 对于高频筛选字段可以适当的建立索引；
- 一个表的索引最好不要超过5个，多了会影响插入修改；
- 不要对值是有限重复的字段建立索引，如性别等；
- 使用组合索引一定要遵守最左原则。
3）替代优化
- 不要使用not in 和<>，这个会破会索引，not in 可以用not exists来代替，<>可以分成两个条件>或者|<等；
- 使用连接(join)来代替子查询；
十一、函数
1、Floor
floor(X)：取整函数
mysql> select floor(1.23)
+-------------+
| floor(1.23) |
+-------------+
| 1 |
+-------------+
mysql> update test set num = floor(num/10)*10 where num >= 20 and num <= 39;
//把二十几和三十几的都改为20和30
2、Substring
截取字符串
substring(str,pos,len)、substring(str,pos)、substring(str from pos)、substring(str from pos for len)
min(str,pos,len)等同
mysql> select substring('今天天气真好！',3);
+-------------------------------+
| substring('今天天气真好！',3) |
+-------------------------------+
| 天气真好！ |
+-------------------------------+
mysql> select substring('今天天气真好！',3,2);
+---------------------------------+
| substring('今天天气真好！',3,2) |
+---------------------------------+
| 天气 |
+---------------------------------+
mysql> select substring('今天天气真好！' from 3);
+------------------------------------+
| substring('今天天气真好！' from 3) |
+------------------------------------+
| 天气真好！ |
+------------------------------------+
mysql> select substring('今天天气真好！' from 3 for 2) as '截取字符串';
+------------+
| 截取字符串 |
+------------+
| 天气 |
+------------+
3、Concat
mysql> select goods_name,concat('荣耀',substring(goods_name from 3)) from goods where goods_name like '__平板';
+------------+---------------------------------------------+
| goods_name | concat('荣耀',substring(goods_name from 3)) |
+------------+---------------------------------------------+
| 苹果平板 | 荣耀平板 |
| 华为平板 | 荣耀平板 |
+------------+---------------------------------------------+
mysql> update goods set goods_name=concat('荣耀',substring(goods_name from 3)) where goods_name like '__平板';
4、Count
求总行数
count(*)和count(1)取的是绝对的行数，哪怕某一行所有字段全为NULL也计算在内
count(列名)取的是该列不为null的所有行的行数
mysql> select count(*) from goods;
mysql> select count(goods_sn) from goods;