diff --git "a/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/config.json" "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/config.json"
index 65884a3a853152360a31e69d2b110e6cdad1de5a..4a5bdfa4019d070a7604220541c17d5842d28f92 100644
--- "a/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/config.json"
+++ "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/config.json"
@@ -1,5 +1,9 @@
 {
   "keywords": [],
   "node_id": "oceanbase-4977bf7616784bfbac4bf88c8a064375",
-  "title": "数据分析"
+  "title": "数据分析",
+  "export": [
+    "max_salary.json",
+    "lost_id.json"
+  ]
 }
\ No newline at end of file
diff --git "a/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/lost_id.json" "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/lost_id.json"
new file mode 100644
index 0000000000000000000000000000000000000000..8df36f02baf224ec2b1d8ad4e7093a008f894377
--- /dev/null
+++ "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/lost_id.json"
@@ -0,0 +1,5 @@
+{
+  "type": "code_options",
+  "author": "刘鑫",
+  "source": "lost_id.md"
+}
\ No newline at end of file
diff --git "a/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/lost_id.md" "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/lost_id.md"
new file mode 100644
index 0000000000000000000000000000000000000000..93578028eee79430929f0e741205d614fa7838f1
--- /dev/null
+++ "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/lost_id.md"
@@ -0,0 +1,61 @@
+# 查找缺失id
+
+一个关系型数据库中，有一个表 list，主键是自增 id。形如：
+
+```sql
+$ select * from list
+id, ...
+----------
+1
+2
+3
+...
+
+```
+
+其中某一行被删除了（不在行首或行尾），哪一条查询能把被删除的哪一行的id找到？
+
+## 答案
+
+```sql
+select l.id
+from (select id - 1 as id from list) as l
+         left join list as r
+                   on l.id = r.id
+where r.id is null
+  and l.id > 0;
+```
+
+## 选项
+
+### 没有处理边界
+
+```sql
+select l.id
+from (select id - 1 as id from list) as l
+         left join list as r
+                   on l.id = r.id
+where r.id is null;
+```
+
+### 没有取外连接
+
+```sql
+select l.id
+from (select id - 1 as id from list) as l
+         join list as r
+                   on l.id = r.id
+where r.id is null
+  and l.id > 0;
+```
+
+### 没有取外连接
+
+```sql
+select l.id
+from (select id - 1 as id from list) as l
+         join list as r
+                   on l.id = r.id
+where r.id is null
+  and l.id > 0;
+```
\ No newline at end of file
diff --git "a/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/max_salary.json" "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/max_salary.json"
new file mode 100644
index 0000000000000000000000000000000000000000..a704b0218d1559c4fe1d4b1b959133915af6b448
--- /dev/null
+++ "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/max_salary.json"
@@ -0,0 +1,5 @@
+{
+  "type": "code_options",
+  "author": "刘鑫",
+  "source": "max_salary.md"
+}
\ No newline at end of file
diff --git "a/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/max_salary.md" "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/max_salary.md"
new file mode 100644
index 0000000000000000000000000000000000000000..de9aedf0863125a48ce987f59f02c712f60cb2df
--- /dev/null
+++ "b/data/3.OceanBase\351\253\230\351\230\266/3.\347\274\226\347\250\213\345\222\214\346\237\245\350\257\242/3.\346\225\260\346\215\256\345\210\206\346\236\220/max_salary.md"
@@ -0,0 +1,51 @@
+# 寻找工资最高的人
+
+有这样一个表：
+
+```sql
+create table employee
+(
+    id integer auto_increment primary key,
+    name varchar(256),
+    department varchar(256),
+    salary integer
+);
+```
+
+下列哪个选项可以找出每个部门工资最高的人，并给出这个人的id，姓名，部门和工资信息？
+
+## 答案
+
+```sql
+select l.id, l.name, l.department, l.salary 
+from employee as l
+    join (select department, max(salary) as salary from employee group by department) as r
+        on l.department = r.department and l.salary = r.salary
+```
+
+## 选项
+
+### 分组错误
+
+```sql
+select id, name, department, salary
+from employee
+group by department
+having salary = max(salary);
+```
+
+### 结构错误
+
+```sql
+select id, name, department, max(salary)
+from employee
+group by department;
+```
+
+### 结构错误
+
+```sql
+select id, name, department, max(salary)
+from employee
+where salary = max(salary);
+```
\ No newline at end of file