【MySQL基础】一文总结MySQL必须把握的常用命令
基础命令MYSQL解释方式
-- 单行注释
/*
多行注释
哈哈哈哈哈
哈哈哈哈
*/
毗连数据库
mysql -u root -p12345678
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退出数据库毗连
使用exit;命令可以退出毗连
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查询MYSQL版本
mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.27 |
+-----------+
1 row in set (0.00 sec)
查看全部数据库
show databases;
https://img-blog.csdnimg.cn/c179e81ad1eb4b17a2caaf816d1468fa.png#pic_center
使用数据库
如果想要操作数据库，须要使用use 数据库名;来选择要操作的数据库
https://img-blog.csdnimg.cn/29f9de5125144c578cc2564cf99b506a.png#pic_center
查看所选择数据库的全部表
show tables;
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查看表的详细信息
使用describe 表名;可以查看表中的字段信息
mysql> describe user;
+--------------+---------------+------+-----+-------------------+-----------------------------------------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------------+------+-----+-------------------+-----------------------------------------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| userName | varchar(256)| YES| | NULL | |
| userAccount| varchar(256)| NO | UNI | NULL | |
| userAvatar | varchar(1024) | YES| | NULL | |
| gender | tinyint | YES| | NULL | |
| userRole | varchar(256)| NO | | user | |
| userPassword | varchar(512)| NO | | NULL | |
| accessKey | varchar(512)| YES| | NULL | |
| secretKey | varchar(512)| YES| | NULL | |
| createTime | datetime | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| updateTime | datetime | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP |
| isDelete | tinyint | NO | | 0 | |
+--------------+---------------+------+-----+-------------------+-----------------------------------------------+
12 rows in set (0.00 sec)
创建数据库
create database 数据库名称 character set 字符编码;
mysql> create database practice character set utf8;
Query OK, 1 row affected, 1 warning (0.01 sec)
-- 已存在的数据库不能重复创建，不然会报错
mysql> create database practice character set utf8;
ERROR 1007 (HY000): Can't create database 'practice'; database exists
-- 使用if not exists，可以判断数据库不存在的时候才创建数据库，这样就不会报错
mysql> create database if not exists practice character set utf8;
Query OK, 1 row affected, 2 warnings (0.01 sec)
如果数据库名字有短横杆，用``包住，否则可能会报错
create database `second-hand-market` character set utf8mb4;
查看创建数据库的语句
mysql> show create database practice;
+----------+------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+------------------------------------------------------------------------------------------------------+
| practice | CREATE DATABASE `practice` /*!40100 DEFAULT CHARACTER SET utf8 */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
修改用户密码
https://img-blog.csdnimg.cn/96dcf79e8de746e98c649b7b635b6a26.png
数据表管理
创建数据表
https://img-blog.csdnimg.cn/375b3c776e464ee0a47c50d1c958991b.png
如：
CREATE TABLE IF NOT EXISTS `student` (
`id` BIGINT NOT NULL auto_increment COMMENT '学号' PRIMARY KEY,
`name` VARCHAR ( 30 ) NOT NULL DEFAULT '匿名' COMMENT '姓名'
) COMMENT '学生表'
查看创建数据表的语句
mysql> use practice;
Database changed
mysql> show create table student;
+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table | Create Table
|+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| student | CREATE TABLE `student` (
`id` bigint NOT NULL AUTO_INCREMENT COMMENT '学号',
`name` varchar(30) NOT NULL DEFAULT '匿名' COMMENT '姓名',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3 COMMENT='学生表' |
+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)
查看表的结构
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name| varchar(30) | NO | | 匿名 | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
修改表名
alter table 旧表名 rename as 新表名;
mysql> alter table student rename as teacher;
Query OK, 0 rows affected (0.02 sec)
删除表
drop table if exists 表名;
mysql> show tables;
+--------------------+| Tables_in_practice |+--------------------+| teacher |+--------------------+1 row in set (0.00 sec)mysql> drop table if exists teacher;Query OK, 0 rows affected (0.02 sec)mysql> show tables;
Empty set (0.00 sec) 数据表字段管理
给指定表增长字段
alter table 表名 add 字段名 列属性;
mysql> alter table teacher add gender bigint;
Query OK, 0 rows affected (0.02 sec)
Records: 0Duplicates: 0Warnings: 0
mysql> desc teacher;
+--------+-------------+------+-----+---------+----------------+
| Field| Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| gender | bigint | YES| | NULL | |
+--------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> alter table teacher add age int(11);
Query OK, 0 rows affected, 1 warning (0.02 sec)
Records: 0Duplicates: 0Warnings: 1
mysql> desc teacher;
+--------+-------------+------+-----+---------+----------------+
| Field| Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| gender | bigint | YES| | NULL | |
| age | int | YES| | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
修改指定表的字段
修改列属性
alter table 表名 modify 字段名 列属性;
mysql> alter table teacher modify age varchar(11);
Query OK, 0 rows affected (0.07 sec)
Records: 0Duplicates: 0Warnings: 0
mysql> desc teacher;
+--------+-------------+------+-----+---------+----------------+
| Field| Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| gender | bigint | YES| | NULL | |
| age | varchar(11) | YES| | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
同时修改字段名和字段属性
alter table 表名 change 旧字段名 新字段名 列属性;
mysql> desc teacher;
+--------+-------------+------+-----+---------+----------------+
| Field| Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| gender | bigint | YES| | NULL | |
| age | varchar(11) | YES| | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> alter table teacher change age age1 int(2);
Query OK, 0 rows affected, 1 warning (0.07 sec)
Records: 0Duplicates: 0Warnings: 1
mysql> desc teacher;
+--------+-------------+------+-----+---------+----------------+
| Field| Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| gender | bigint | YES| | NULL | |
| age1 | int | YES| | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
删除指定表的字段
mysql> desc teacher;
+--------+-------------+------+-----+---------+----------------+
| Field| Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| gender | bigint | YES| | NULL | |
| age1 | int | YES| | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> alter table teacher drop gender;
Query OK, 0 rows affected (0.06 sec)
Records: 0Duplicates: 0Warnings: 0
mysql> desc teacher;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name| varchar(30) | NO | | 匿名 | |
| age1| int | YES| | NULL | |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
给表添加外键
创建表的时间增长外键
-- 创建专业表
CREATE TABLE IF NOT EXISTS `major` (
`id` BIGINT NOT NULL auto_increment COMMENT '专业id' PRIMARY KEY,
`name` VARCHAR ( 30 ) NOT NULL COMMENT '专业名称'
) COMMENT '专业表'
-- 创建学生表，并将学生表的major_id声明为外键，引用专业表的id字段
CREATE TABLE IF NOT EXISTS `student` (
`id` BIGINT NOT NULL auto_increment COMMENT '学号' PRIMARY KEY,
`name` VARCHAR ( 30 ) NOT NULL DEFAULT '匿名' COMMENT '姓名',
`major_id` BIGINT NOT NULL COMMENT '专业id',
key `FK_majorId` (`major_id`),
CONSTRAINT `FK_majorId` FOREIGN KEY (`major_id`) REFERENCES `major`(`id`)
) COMMENT '学生表'
https://img-blog.csdnimg.cn/2f8897ec9bb9489ea3277378318564a4.png#pic_center
给已有表添加外键
ALTER TABLE 表名 ADD CONSTRAINT 约束名 FOREIGN KEY(作为外键的列的字段名) REFERENCES 引用哪个表(哪个字段)
【案例】
ALTER TABLE `student` ADD CONSTRAINT `FK_majorId` FOREIGN KEY(`major_id`) REFERENCES `major`(`id`);
外键使用建议
当使用了外键时，如果须要删除被引用表的记录，须要先删除引用表的记录。如上面的例子所示，如果须要删除一个专业，须要先删除这个专业所对应的学生。
建议：使用外键束缚会让开发者很痛楚，测试数据不方便，建议不使用外键
数据插入语句 INSERT
数据插入
insert into `表名` (`字段名1`,`字段名2`) values('字段值1','字段值2');
一次性插入多条数据
insert into `表名` (`字段名1`,`字段名2`) values('字段值11','字段值12'),('字段值21','字段值22'),('字段值31','字段值32');
案例
mysql> desc student;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | 匿名 | |
| major_id | bigint | NO | MUL | NULL | |
+----------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> desc major;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| name| varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
--insert into `表名` (`字段名`) values('字段值');
mysql> insert into `major` (`name`) values('计算机科学');
Query OK, 1 row affected (0.01 sec)
mysql> insert into `major` (`name`) values('工业工程');
Query OK, 1 row affected (0.01 sec)
mysql> select * from major;
+----+-----------------+
| id | name |
+----+-----------------+
|1 | 计算机科学 |
|2 | 工业工程 |
+----+-----------------+
2 rows in set (0.00 sec)
-- 插入多条数据
mysql> insert into `major` (`name`) values('自动化'),('机械工程'),('工业设计');
Query OK, 3 rows affected (0.01 sec)
Records: 3Duplicates: 0Warnings: 0
mysql> select * from major;
+----+-----------------+
| id | name |
+----+-----------------+
|1 | 计算机科学 |
|2 | 工业工程 |
|3 | 自动化 |
|4 | 机械工程 |
|5 | 工业设计 |
+----+-----------------+
5 rows in set (0.00 sec)
mysql> insert into `student` (`name`,`major_id`) values('小明','1');
Query OK, 1 row affected (0.01 sec)
mysql> select * from student;
+----+--------+----------+
| id | name | major_id |
+----+--------+----------+
|1 | 小明 | 1 |
+----+--------+----------+
1 row in set (0.00 sec)
-- 插入数据的时候，不一定要给表的所有字段赋值，只赋值部分字段也可以，前提是省略的字段可以为空
mysql> insert into `student` (`major_id`) values('1');
Query OK, 1 row affected (0.01 sec)
-- 插入数据的时候，没有写入学生的名字，MYSQL会自动填入默认值“匿名”
mysql> select * from student;
+----+--------+----------+
| id | name | major_id |
+----+--------+----------+
|1 | 小明 | 1 |
|2 | 匿名 | 1 |
+----+--------+----------+
2 rows in set (0.00 sec)
数据更新语句 UPDATE
没有指定匹配条件的话，会全部表的全部记录
mysql> select * from major;
+----+-----------------+
| id | name |
+----+-----------------+
|1 | 计算机科学 |
|2 | 工业工程 |
|3 | 自动化 |
|4 | 机械工程 |
|5 | 工业设计 |
+----+-----------------+
5 rows in set (0.00 sec)
mysql> update major set name='智能制造';
Query OK, 5 rows affected (0.01 sec)
Rows matched: 5Changed: 5Warnings: 0
mysql> select * from major;
+----+--------------+
| id | name |
+----+--------------+
|1 | 智能制造 |
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
|5 | 智能制造 |
+----+--------------+
5 rows in set (0.00 sec)
根据条件来修改记录
mysql> update major set name='智能科学与技术' where id = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1Changed: 1Warnings: 0
mysql> select * from major;
+----+-----------------------+
| id | name |
+----+-----------------------+
|1 | 智能科学与技术 |
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
|5 | 智能制造 |
+----+-----------------------+
5 rows in set (0.00 sec)
一次性修改多个字段的值
mysql> select * from student;
+----+--------+----------+
| id | name | major_id |
+----+--------+----------+
|1 | 小明 | 1 |
|2 | 匿名 | 1 |
+----+--------+----------+
2 rows in set (0.00 sec)
mysql> update student set name='李华',major_id=2 where id = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1Changed: 1Warnings: 0
mysql> select * from student;
+----+--------+----------+
| id | name | major_id |
+----+--------+----------+
|1 | 李华 | 2 |
|2 | 匿名 | 1 |
+----+--------+----------+
2 rows in set (0.00 sec)
稍微高级一点的使用
update load_product,product set load_product.product_id = product.id where load_product.code=product.code
where条件
where条件可以使用的操作符
https://img-blog.csdnimg.cn/36c5838cdab343b98dea583871f3b0e4.png#pic_center
多个条件共同使用，使用and毗连，如where id=1 and name=‘李华’
mysql> select id,name as 专业名称 from major;
+----+-----------------------+
| id | 专业名称 |
+----+-----------------------+
|1 | 智能科学与技术 |
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
|5 | 智能制造 |
+----+-----------------------+
5 rows in set (0.00 sec)
mysql> select id,name as 专业名称 from major where name='智能制造';
+----+--------------+
| id | 专业名称 |
+----+--------------+
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
|5 | 智能制造 |
+----+--------------+
4 rows in set (0.00 sec)
mysql> select id,name as 专业名称 from major where name!='智能制造';
+----+-----------------------+
| id | 专业名称 |
+----+-----------------------+
|1 | 智能科学与技术 |
+----+-----------------------+
1 row in set (0.00 sec)
mysql> select id,name as 专业名称 from major where not name='智能制造';
+----+-----------------------+
| id | 专业名称 |
+----+-----------------------+
|1 | 智能科学与技术 |
+----+-----------------------+
1 row in set (0.00 sec)
mysql> select id,name as 专业名称 from major where name='智能制造' and id =2;
+----+--------------+
| id | 专业名称 |
+----+--------------+
|2 | 智能制造 |
+----+--------------+
1 row in set (0.00 sec)
mysql> select id,name as 专业名称 from major where id < 2;
+----+-----------------------+
| id | 专业名称 |
+----+-----------------------+
|1 | 智能科学与技术 |
+----+-----------------------+
1 row in set (0.00 sec)
mysql> select id,name as 专业名称 from major where id >= 2;
+----+--------------+
| id | 专业名称 |
+----+--------------+
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
|5 | 智能制造 |
+----+--------------+
4 rows in set (0.00 sec)
mysql> select id,name as 专业名称 from major where id >= 2 and id <= 4;
+----+--------------+
| id | 专业名称 |
+----+--------------+
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
+----+--------------+
3 rows in set (0.00 sec)
mysql> select id,name as 专业名称 from major where id = 2 or id = 4;
+----+--------------+
| id | 专业名称 |
+----+--------------+
|2 | 智能制造 |
|4 | 智能制造 |
+----+--------------+
2 rows in set (0.00 sec)
判空
固然，还可以用来判空大概非空，并不是直接=null，而是is null和is not null
UPDATE sys_user
SET avatar = concat( "https://hahaha/", FLOOR(RAND()*29+1), ".png" )
WHERE
avatar IS NULL
OR avatar = "";
and和or的使用
SELECT
*
FROM
chat
WHERE
( from_who = "admin" AND to_who = "user1" )
OR ( to_who = "admin" AND from_who = "user1" )
ORDER BY
create_time DESC;
https://img-blog.csdnimg.cn/8919c08cb987445abf0af7547d67b6b5.png#pic_center
数据删除 DELETE
删除全部数据
delete from 表名;
使用delete删除全部数据，如果重启数据库，会出现如下现象
[*]InnoDB 自增列会从1开始（存在内存中，断电即失）
[*]MyISAM 自增列继承从上一个自增量开始（存在文件中，不会丢失）
删除指定数据
delete from 表名 where 条件;
数据表清空 TRUNCATE
清空一个数据表的全部数据，自增id计数器重新恢复到1，表的结构和索引束缚不会改变
truncate 表名
数据查询语言Data Query LANGUAGE(DQL) SELECT
查询一个表中的全部数据
select * from 表名;
查询指定字段的数据
select 字段1,字段2,字段3 from 表名;
注意：能查询部门字段的，千万不要查询*，这样会增长查询时间
给字段取别名
mysql> select name from major;
+-----------------------+
| name |
+-----------------------+
| 智能科学与技术 |
| 智能制造 |
| 智能制造 |
| 智能制造 |
| 智能制造 |
+-----------------------+
5 rows in set (0.00 sec)
mysql> select name as 专业名称 from major;
+-----------------------+
| 专业名称 |
+-----------------------+
| 智能科学与技术 |
| 智能制造 |
| 智能制造 |
| 智能制造 |
| 智能制造 |
+-----------------------+
5 rows in set (0.00 sec)
给表取别名
mysql> select student.id as 学号,student.name as 姓名,major.name as 专业 from student left join major on student.major_id = major.id;
+--------+--------+-----------------------+
| 学号 | 姓名 | 专业 |
+--------+--------+-----------------------+
| 1 | 李华 | 智能制造 |
| 2 | 匿名 | 智能科学与技术 |
+--------+--------+-----------------------+
2 rows in set (0.00 sec)
mysql> select s.id as 学号,s.name as 姓名,m.name as 专业 from student as s left join major as m on s.major_id = m.id;
+--------+--------+-----------------------+
| 学号 | 姓名 | 专业 |
+--------+--------+-----------------------+
| 1 | 李华 | 智能制造 |
| 2 | 匿名 | 智能科学与技术 |
+--------+--------+-----------------------+
2 rows in set (0.00 sec)
取别名可以更方便开发者编写sql语句
字符串拼接
mysql> select concat('专业名称：',name) from major;
+--------------------------------------+
| concat('专业名称：',name) |
+--------------------------------------+
| 专业名称：智能科学与技术 |
| 专业名称：智能制造 |
| 专业名称：智能制造 |
| 专业名称：智能制造 |
| 专业名称：智能制造 |
+--------------------------------------+
5 rows in set (0.00 sec)
查询效果数据去重
重复的数据只体现一条
mysql> select name as 专业名称 from major;
+-----------------------+
| 专业名称 |
+-----------------------+
| 智能科学与技术 |
| 智能制造 |
| 智能制造 |
| 智能制造 |
| 智能制造 |
+-----------------------+
5 rows in set (0.00 sec)
mysql> select distinct name as 专业名称 from major;
+-----------------------+
| 专业名称 |
+-----------------------+
| 智能科学与技术 |
| 智能制造 |
+-----------------------+
2 rows in set (0.00 sec)
查询时增长计算
mysql> select id,name as 专业名称 from major;
+----+-----------------------+
| id | 专业名称 |
+----+-----------------------+
|1 | 智能科学与技术 |
|2 | 智能制造 |
|3 | 智能制造 |
|4 | 智能制造 |
|5 | 智能制造 |
+----+-----------------------+
5 rows in set (0.00 sec)
-- 将所有数据的 id 增加 1
mysql> select id+1,name as 专业名称 from major;
+------+-----------------------+
| id+1 | 专业名称 |
+------+-----------------------+
| 2 | 智能科学与技术 |
| 3 | 智能制造 |
| 4 | 智能制造 |
| 5 | 智能制造 |
| 6 | 智能制造 |
+------+-----------------------+
5 rows in set (0.00 sec)
含糊查询
https://img-blog.csdnimg.cn/7a00d9c5ce764987b16a943278b0f56f.png
https://img-blog.csdnimg.cn/9e081c37433247e3b97e1c13cbb5d829.png#pic_center
毗连查询
七种毗连方式
https://blog.csdn.net/laodanqiu/article/details/131233741
自毗连
用途：一个表同时存储了父类数据和子类数据，如省市区表同时存储了中国的全部省、市、区的数据，希望查询出广东省下面的全部城市
mysql> desc province_city_region;
+-------------+-------------+------+-----+-------------------+-----------------------------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+-------------------+-----------------------------------------------+
| id | bigint | NO | PRI | NULL | auto_increment |
| create_time | datetime | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| update_time | datetime | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP |
| is_deleted| tinyint | YES| | 0 | |
| name | varchar(50) | YES| | NULL | |
| type | tinyint | YES| | NULL | |
| parent_id | bigint | YES| | NULL | |
+-------------+-------------+------+-----+-------------------+-----------------------------------------------+
7 rows in set (0.00 sec)
mysql> select a.id,a.name as 市名称,b.name as 省名称 from province_city_region as a,province_city_region as b where b.name="广东省" and a.parent_id=b.id;
+------+-----------+-----------+
| id | 市名称 | 省名称 |
+------+-----------+-----------+
| 4792 | 茂名市 | 广东省 |
| 4798 | 湛江市 | 广东省 |
| 4808 | 东莞市 | 广东省 |
| 4809 | 江门市 | 广东省 |
| 4817 | 清远市 | 广东省 |
| 4826 | 佛山市 | 广东省 |
| 4832 | 阳江市 | 广东省 |
| 4837 | 汕头市 | 广东省 |
| 4845 | 河源市 | 广东省 |
| 4852 | 珠海市 | 广东省 |
| 4856 | 汕尾市 | 广东省 |
| 4861 | 深圳市 | 广东省 |
| 4868 | 梅州市 | 广东省 |
| 4877 | 揭阳市 | 广东省 |
| 4883 | 韶关市 | 广东省 |
| 4894 | 惠州市 | 广东省 |
| 4900 | 潮州市 | 广东省 |
| 4904 | 广州市 | 广东省 |
| 4916 | 肇庆市 | 广东省 |
| 4925 | 中山市 | 广东省 |
| 4926 | 云浮市 | 广东省 |
+------+-----------+-----------+
21 rows in set (0.00 sec)
分页
【查询语句】limit 数据索引起始值 数据量的巨细
limit 0,5:查询的是第0,1,2,3,4条数据
limit 2,5:查询的是第2,3,4,5,6条数据
排序
【查询语句】order by 字段 ASC / DESC
[*]ASC（升序）
[*]DESC（降序）
mysql> select * from province_city_region order by id asc limit 0,10;
+------+---------------------+---------------------+------------+-----------+------+-----------+
| id | create_time | update_time | is_deleted | name | type | parent_id |
+------+---------------------+---------------------+------------+-----------+------+-----------+
| 2928 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 山东省 | 0 | 0 |
| 2929 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 莱芜市 | 1 | 2928 |
| 2930 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 莱城区 | 2 | 2929 |
| 2931 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 钢城区 | 2 | 2929 |
| 2932 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 济南市 | 1 | 2928 |
| 2933 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 历城区 | 2 | 2932 |
| 2934 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 历下区 | 2 | 2932 |
| 2935 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 长清区 | 2 | 2932 |
| 2936 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 平阴县 | 2 | 2932 |
| 2937 | 2023-02-10 20:38:54 | 2023-02-10 20:38:54 | 0 | 章丘市 | 1 | 2932 |
+------+---------------------+---------------------+------------+-----------+------+-----------+
10 rows in set (0.00 sec)
mysql> select * from province_city_region order by id desc limit 0,10;
+------+---------------------+---------------------+------------+--------------------------+------+-----------+
| id | create_time | update_time | is_deleted | name | type | parent_id |
+------+---------------------+---------------------+------------+--------------------------+------+-----------+
| 5851 | 2023-02-10 20:39:11 | 2023-02-10 20:39:11 | 0 | 天峨县 | 2 | 5840 |
| 5850 | 2023-02-10 20:39:11 | 2023-02-10 20:39:11 | 0 | 凤山县 | 2 | 5840 |
| 5849 | 2023-02-10 20:39:11 | 2023-02-10 20:39:11 | 0 | 南丹县 | 2 | 5840 |
| 5848 | 2023-02-10 20:39:11 | 2023-02-10 20:39:11 | 0 | 环江毛南族自治县 | 2 | 5840 |
| 5847 | 2023-02-10 20:39:11 | 2023-02-10 20:39:11 | 0 | 巴马瑶族自治县 | 2 | 5840 |
| 5846 | 2023-02-10 20:39:11 | 2023-02-10 20:39:10 | 0 | 东兰县 | 2 | 5840 |
| 5845 | 2023-02-10 20:39:11 | 2023-02-10 20:39:10 | 0 | 金城江区 | 2 | 5840 |
| 5844 | 2023-02-10 20:39:11 | 2023-02-10 20:39:10 | 0 | 罗城仫佬族自治县 | 2 | 5840 |
| 5843 | 2023-02-10 20:39:11 | 2023-02-10 20:39:10 | 0 | 宜州市 | 1 | 5840 |
| 5842 | 2023-02-10 20:39:11 | 2023-02-10 20:39:10 | 0 | 都安瑶族自治县 | 2 | 5840 |
+------+---------------------+---------------------+------------+--------------------------+------+-----------+
10 rows in set (0.00 sec)
子查询
https://img-blog.csdnimg.cn/aab8105f026d48689c500dbe477c7b9f.png#pic_center
https://img-blog.csdnimg.cn/8c1b3d69fc1040a5bdf5b1ba1728f427.png#pic_center
注意：子查询的效率高于连表查询
查询常用函数
【数学运算】
SELECT ABS(-8)--绝对值
SELECT CEILING(9.4)--向上取整
SELECT FLOOR(9.4)--向下取整
SELECT RAND()一一返回一个0~1之间的随机数
SELECT SIGN (10)一一判断一个数的符号(负数返回-1，正数返回1,0返回0)
【字符串函数】
SELECT CHAR_LENGTH('即使再小的帆也能远航')--字符串长度
SELECT CONCAT('哈'，'哈'，'哈')--拼接字符串
SELECT INSERT('我爱编程helloworld',1,2,'超级热爱')--从某个位置开始替换某个长度
SELECT LOWER('Abc')--转化为小写字母
SELECT UPPER('Abc')--转化为大写字母
SELECT INSTR('Abc','bc')--返回第一次出现的子串的索引
SELECT REPLACE('你好'，'好'，'坏')--替换出现的指定字符串
SELECT SUBSTR('你吃饭了吗'，1,3)--返回指定的子字符串（源字符串，截取的位置，截取的长度）
SELECT REVERSE('我和你')--反转
-- 查询学生，将查询出来的数据姓氏进行替换
SELECT REPLACE(student_name,'王'，'玩')FROM student
【时间和日期函数】
SELECT CURRENT_DATE()--获取当前日期
SELECT CURDATE()-一获取当前日期
SELECT NOW()--获取当前的时间
SELECT LOCALTIME()--本地时间
SELECT SYSDATE()-一系统时间
SELECT YEAR(NOW())
SELECT MONTH(NOW())
SELECT DAY(NOW())
SELECT HOUR(NOW())
SELECT MINUTE(NOW())
SELECT SECOND(NOW())
【数据库相干】
SELECT SYSTEM USER();
SELECT USER();
SELECT VERSION();--查询数据库版本
【统计相干】
都能够统计表中的数据（想查询一个表中有多少个记录，就使用这个cout())
SELECT COUNT(`BornDate`) FROM student;--Count(字段)，会忽略所有的nul1值
SELECT COUNT(*) FROM student;--Count(*),不会忽略null值，本质计算行数
SELECT COUNT(1) FROM result;--Count(1),不会忽略忽略所有的nul1值，本质计算行数
SELECT SUM(`StudentResult`) AS 总和 FROM result;
SELECT AVG(`StudentResult`) AS 平均分 FROM result;
SELECT MAX(`StudentResult`) AS 最高分 FROM result;
SELECT MIN(`StudentResult`) As 最低分 FROM result;
注意事项
UPDATE sys_user
SET avatar = concat( "https://hahaha/", FLOOR(RAND()*29+1), ".png" )
WHERE
avatar IS NULL
OR avatar = "";
使用函数可能导致字段的索引失效，造成效率下降，建议直接读出来，然后用java举行处理
分组过滤
mysql> select name,gender from user limit 0,10;
+-----------------+--------+
| name | gender |
+-----------------+--------+
| 系统管理员 | 0 |
| 企业管理员 | 0 |
| 门店管理员 | 0 |
| 郗淑 | 0 |
| 柳之 | 1 |
| 夏侯之 | 1 |
| 吉滢 | 0 |
| 独孤杰 | 1 |
| 蒙飘 | 0 |
| 卫柔 | 0 |
+-----------------+--------+
10 rows in set (0.00 sec)
-- 根据 gender 进行分组
mysql> select name,gender from user group by gender limit 0,10;
+-----------------+--------+
| name | gender |
+-----------------+--------+
| 系统管理员 | 0 |
| 柳之 | 1 |
+-----------------+--------+
2 rows in set (0.01 sec)
https://img-blog.csdnimg.cn/e406b10deaef4fafbf0b11c811e0bbc7.png#pic_center
能使用where，就不要使用having，否则可能导致索引失效
SELECT语法完整结构
https://img-blog.csdnimg.cn/030068e138aa48feb4d6e6fb33e11227.png
https://img-blog.csdnimg.cn/fe8eb72f032f49b38f021740c4750c6e.png#pic_center
[]：代表可选
{}：代表必选
数据加密
【建表sql】
DROP TABLE
IF
EXISTS `user`;
CREATE TABLE `user` (
`id` BIGINT NOT NULL auto_increment COMMENT '主键' PRIMARY KEY,
`create_time` datetime DEFAULT CURRENT_TIMESTAMP NOT NULL COMMENT '创建时间',
`update_time` datetime DEFAULT CURRENT_TIMESTAMP NOT NULL ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
`is_deleted` TINYINT DEFAULT 0 NULL COMMENT '是否删除 0：未删除 1：已删除',
`username` VARCHAR ( 50 ) DEFAULT NULL COMMENT '用户名',
`password` VARCHAR ( 255 ) NOT NULL COMMENT '密码',
`gender` TINYINT DEFAULT 0 NULL COMMENT '性别 0：男 1：女',
`age` INT DEFAULT NULL COMMENT '年龄'
) COMMENT '用户表';
-- 插入数据
mysql> insert into user(`username`,`password`,`gender`,`age`) values('admin','123456',0,18),('hello','123456',0,28),('word','123456',1,17);
Query OK, 3 rows affected (0.01 sec)
Records: 3Duplicates: 0Warnings: 0
【密码MD5加密操作】
mysql> select * from user;
+----+---------------------+---------------------+------------+----------+----------+--------+------+
| id | create_time | update_time | is_deleted | username | password | gender | age|
+----+---------------------+---------------------+------------+----------+----------+--------+------+
|1 | 2023-07-05 10:16:16 | 2023-07-05 10:16:16 | 0 | admin | 123456 | 0 | 18 |
|2 | 2023-07-05 10:16:16 | 2023-07-05 10:16:16 | 0 | hello | 123456 | 0 | 28 |
|3 | 2023-07-05 10:16:16 | 2023-07-05 10:16:16 | 0 | word | 123456 | 1 | 17 |
+----+---------------------+---------------------+------------+----------+----------+--------+------+
3 rows in set (0.00 sec)
-- 加密id=1的数据的密码
mysql> update user set password=MD5(password) where id=1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1Changed: 1Warnings: 0
mysql> select * from user;
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
| id | create_time | update_time | is_deleted | username | password | gender | age|
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
|1 | 2023-07-05 10:16:16 | 2023-07-05 10:18:38 | 0 | admin | e10adc3949ba59abbe56e057f20f883e | 0 | 18 |
|2 | 2023-07-05 10:16:16 | 2023-07-05 10:16:16 | 0 | hello | 123456 | 0 | 28 |
|3 | 2023-07-05 10:16:16 | 2023-07-05 10:16:16 | 0 | word | 123456 | 1 | 17 |
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
3 rows in set (0.00 sec)
-- 加密所有数据的密码
mysql> update user set password=MD5(password);
Query OK, 3 rows affected (0.01 sec)
Rows matched: 3Changed: 3Warnings: 0
mysql> select * from user;
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
| id | create_time | update_time | is_deleted | username | password | gender | age|
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
|1 | 2023-07-05 10:16:16 | 2023-07-05 10:19:01 | 0 | admin | 14e1b600b1fd579f47433b88e8d85291 | 0 | 18 |
|2 | 2023-07-05 10:16:16 | 2023-07-05 10:19:01 | 0 | hello | e10adc3949ba59abbe56e057f20f883e | 0 | 28 |
|3 | 2023-07-05 10:16:16 | 2023-07-05 10:19:01 | 0 | word | e10adc3949ba59abbe56e057f20f883e | 1 | 17 |
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
3 rows in set (0.00 sec)
-- 插入数据的时候就执行加密
mysql> insert into user(`username`,`password`,`gender`,`age`) values('md5',MD5('123456'),0,18);
Query OK, 1 row affected (0.01 sec)
mysql> select * from user;
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
| id | create_time | update_time | is_deleted | username | password | gender | age|
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
|1 | 2023-07-05 10:16:16 | 2023-07-05 10:19:01 | 0 | admin | 14e1b600b1fd579f47433b88e8d85291 | 0 | 18 |
|2 | 2023-07-05 10:16:16 | 2023-07-05 10:19:01 | 0 | hello | e10adc3949ba59abbe56e057f20f883e | 0 | 28 |
|3 | 2023-07-05 10:16:16 | 2023-07-05 10:19:01 | 0 | word | e10adc3949ba59abbe56e057f20f883e | 1 | 17 |
|4 | 2023-07-05 10:19:46 | 2023-07-05 10:19:46 | 0 | md5 | e10adc3949ba59abbe56e057f20f883e | 0 | 18 |
+----+---------------------+---------------------+------------+----------+----------------------------------+--------+------+
4 rows in set (0.00 sec)
在存储密码这种数据时，一定要举行加密，直接使用MD5加密也还是不安全的，可以被暴力破解，可以使用更加安全的盐值加密
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