diff --git a/blog/php-mysql/index.md b/blog/php-mysql/index.md
index e02b8964e51efee44db99b60846cdc4febbf3af0..2c21cb2eaab6b127a89e6df093de63e0b3030530 100644
--- a/blog/php-mysql/index.md
+++ b/blog/php-mysql/index.md
@@ -45,3 +45,5 @@
 [连接查询 join](blog/php-mysql/sql-join.md)
 
 [子查询 sub query](blog/php-mysql/sql-subquery.md)
+
+[数据库备份与还原](blog/php-mysql/sql-bak.md)
diff --git a/blog/php-mysql/sql-bak.md b/blog/php-mysql/sql-bak.md
new file mode 100644
index 0000000000000000000000000000000000000000..5f781ff48347dea9a3dfc4ac87e15eaf77de5b7c
--- /dev/null
+++ b/blog/php-mysql/sql-bak.md
@@ -0,0 +1,93 @@
+# 数据库备份与还原
+
+## 1、数据库备份
+
+备份的结果都是SQL指令
+
+mysqldump：专门用于备份SQL的客户端
+
+SQL备份：表结构 + 数据
+
+缺点：
+
+1. 会产生的备份文件特别大
+2. 不适合特大型数据备份
+3. 不适合数据变更频繁的数据库备份
+
+基本语法
+
+```bash
+> mysqldump -hPup 数据库名字 [表1 [表2]] > 备份文件地址
+```
+
+备份可以有3种形式
+
+1. 整库备份 只需太提供数据库名字
+2. 单表备份 数据库后跟一张表
+3. 多表备份 数据库后跟多张表
+
+示例
+```bash
+# 整库备份
+> mysqldump -hlocalhost -P3306 -uroot -p123456 mydatabase > mydatabase.bak.sql
+
+# 单表备份
+> mysqldump -hlocalhost -P3306 -uroot -p123456 mydatabase my_student > mydatabase.my_student.bak.sql
+
+# 多表备份
+> mysqldump -hlocalhost -P3306 -uroot -p123456 mydatabase my_student my_class > mydatabase.my_student__my_class.bak.sql
+```
+
+备份文件内容
+
+```sql
+-- 删除已存在的表
+DROP TABLE IF EXISTS `my_student`;
+
+
+-- 创建表结构
+SET character_set_client = utf8mb4 ;
+CREATE TABLE `my_student` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `name` varchar(10) COLLATE utf8mb4_general_ci DEFAULT NULL,
+  `class_id` int(11) DEFAULT NULL,
+  `age` int(11) DEFAULT NULL,
+  `gender` int(11) DEFAULT NULL,
+  PRIMARY KEY (`id`)
+) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;
+
+
+-- 插入数据
+LOCK TABLES `my_student` WRITE;
+INSERT INTO `my_student` VALUES (1,'刘备',1,18,2),(2,'李四',1,19,1),(3,'王五',2,20,2),(4,'张飞',2,21,1),(5,'关羽',NULL,22,2),(6,'曹操',1,20,NULL);
+UNLOCK TABLES;
+```
+
+## 2、数据还原
+
+mysqldump备份的数据文件，没有关于数据库本身的操作，都是针对表级别的操作，当进行数据还原，必须指定数据库
+
+方式一：mysql客户端
+
+```bash
+# 不用登录，直接操作
+> mysql -hPup 数据库 < SQL文件位置
+
+mysql -hlocalhost -P3306 -uroot -p123456 mydatabase2 < mydatabase.bak.sql
+```
+
+方式二：SQL指令导入
+
+```sql
+-- 首先进入到对应的数据库
+mysql> source SQL文件位置
+
+source mydatabase.bak.sql;
+```
+
+方式三：手动复制粘贴（不推荐）
+
+打开备份文件，复制所有SQL指令，粘贴到mysql命令行中执行
+
+
+https://www.bilibili.com/video/BV1Vx411g7uJ?p=54&spm_id_from=pageDriver
\ No newline at end of file
diff --git a/blog/php-mysql/sql-subquery.md b/blog/php-mysql/sql-subquery.md
index 5a68abe7cf2e68dbcc264ef6a82d9eeb36921228..3452c243afc341a65b10f30247f1a3816e4d06a3 100644
--- a/blog/php-mysql/sql-subquery.md
+++ b/blog/php-mysql/sql-subquery.md
@@ -217,28 +217,174 @@ select * from (
 
 ```
 
-https://www.bilibili.com/video/BV1Vx411g7uJ?p=51&spm_id_from=pageDriver
+## 6、exists子查询
 
+返回结果只有0或者1，1代表成立，0代表不成立
 
+### 6.1、基本语法
 
+```sql
+where exists (查询语句)
+
+-- 永远为真
+where 1;
+```
+
+### 6.2、示例
 
+```sql
+-- 查询有学生的所有班级
+select * from my_class as c where exists (
+    select id from my_student as s where s.class_id = c.id
+);
++----+--------+
+| id | name   |
++----+--------+
+|  1 | 一班   |
+|  2 | 二班   |
++----+--------+
+```
+
+## 7、子查询中的特定关键字
+
+```sql
+mysql> select * from my_student;
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  5 | 关羽   |        1 |   22 |      2 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
 
+mysql> select id from my_class;
++----+
+| id |
++----+
+|  1 |
+|  3 |
+|  2 |
++----+
+```
 
+### 7.1、in
 
+```sql
+主查询 where 条件 in (列子查询)
 
+select * from my_student where class_id in (select id from my_class);
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  5 | 关羽   |        1 |   22 |      2 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
+```
 
+### 7.2、any
 
+```sql
+-- 查询结果中有任意一个匹配即可，等价于in
+主查询 where 条件 any (列子查询)
 
+select * from my_student where class_id = any (select id from my_class);
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  5 | 关羽   |        1 |   22 |      2 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
 
+-- 不等于任意一个
+主查询 where 条件 any <> (列子查询)
+select * from my_student where class_id <> any (select id from my_class);
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  5 | 关羽   |        1 |   22 |      2 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
+```
 
+### 7.3、some
 
+与any完全一样
 
+### 7.4、all
 
+```sql
+-- 等于其中所有
+=all(列子查询)
 
+select * from my_student where class_id = all (select id from my_class);
+Empty set (0.00 sec)
 
+select * from my_class where id = all (select class_id from my_student);
+Empty set (0.00 sec)
 
+-- 不等于其中所有
+<>all(列子查询)
+select * from my_student where class_id <> all (select id from my_class);
+Empty set (0.00 sec)
 
+select * from my_class where id <> all (select class_id from my_student);
++----+--------+
+| id | name   |
++----+--------+
+|  3 | 三班   |
++----+--------+
+```
 
+### 7.5、值为null
 
+如果值为null,不参与匹配
+```sql
+mysql> select * from my_student;
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  5 | 关羽   |     NULL |   22 |      2 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
 
+mysql> select * from my_student where class_id = any (select id from my_class);
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
 
+mysql> select * from my_student where class_id <> any (select id from my_class);
++----+--------+----------+------+--------+
+| id | name   | class_id | age  | gender |
++----+--------+----------+------+--------+
+|  1 | 刘备   |        1 |   18 |      2 |
+|  2 | 李四   |        1 |   19 |      1 |
+|  3 | 王五   |        2 |   20 |      2 |
+|  4 | 张飞   |        2 |   21 |      1 |
+|  6 | 曹操   |        1 |   20 |   NULL |
++----+--------+----------+------+--------+
+```