diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/pivot.json" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/case.json"
similarity index 83%
rename from "data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/pivot.json"
rename to "data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/case.json"
index e3606514f2cac9268a744e730a6ce971bc26e451..232607bcf6575397e7d88beca18d41a7b4a657a6 100644
--- "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/pivot.json"	
+++ "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/case.json"	
@@ -1,7 +1,7 @@
 {
   "type": "code_options",
   "author": "ccat",
-  "source": "pivot.md",
+  "source": "case.md",
   "notebook_enable": false,
   "exercise_id": "d61198987832488ab53e8a18f7337946"
 }
\ No newline at end of file
diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/case.md" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/case.md"
new file mode 100644
index 0000000000000000000000000000000000000000..2a009e3aeaae5a4ec6467579af5cc9947125840b
--- /dev/null
+++ "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/case.md"	
@@ -0,0 +1,80 @@
+# 透视表
+
+Goods 表结构如下
+
+```mysql
+create table goods(
+                      id int primary key auto_increment,
+                      category_id int,
+                      category varchar(64),
+                      name varchar(256),
+                      price decimal(12, 4),
+                      stock int,
+                      upper_time timestamp
+)
+```
+
+Joe 想要做一个报表，只需要显示商品名和价格分级，其中不足10元的是 cheap, 超过1000的是expensive，其它的是 
+normal，这个查询应该怎么写？
+
+## 答案
+
+```mysql
+select name,
+       case 
+           when price < 10 then 'cheap'
+           when price > 1000 then 'expensive'
+           else 'normal'
+       end as level
+from goods;
+```
+
+## 选项
+
+### A
+
+```mysql
+select name,
+       case price
+           when  < 10 then 'cheap'
+           when  > 1000 then 'expensive'
+           else 'normal'
+           end as level
+from goods;
+```
+
+### B
+
+```mysql
+select name,
+       case
+           when price < 10  'cheap'
+           when price > 1000 'expensive'
+           else 'normal'
+           end as level
+from goods;
+```
+
+### C
+
+```mysql
+select name,
+       case
+           when price < 10 then 'cheap'
+           when price > 1000 then 'expensive'
+           case _ 'normal'
+           end as level
+from goods;
+```
+
+### C
+
+```mysql
+select name,
+       case
+           when price < 10 then 'cheap'
+           when price > 1000 then 'expensive'
+           case _ 'normal'
+           end as level
+from goods;
+```
\ No newline at end of file
diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/config.json" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/config.json"
index 61478f67db57633e4537e9e3f8264ba5e595d219..d7cd4d32964504e2155851c57b839ce930a40a3e 100644
--- "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/config.json"	
+++ "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/config.json"	
@@ -1,9 +1,13 @@
 {
   "node_id": "mysql-8e6cd4d5f4b446a2bc3f5402de9bd49c",
-  "keywords": ["case", "pivot", "透视表"],
+  "keywords": [
+    "case",
+    "pivot",
+    "透视表"
+  ],
   "children": [],
   "export": [
-    "pivot.json"
+    "case.json"
   ],
   "keywords_must": [],
   "keywords_forbid": [],
diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/pivot.md" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/pivot.md"
deleted file mode 100644
index b1e6373667e2cb16d3f83bbb9f8273f7296e4164..0000000000000000000000000000000000000000
--- "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/3.CASE/pivot.md"	
+++ /dev/null
@@ -1,89 +0,0 @@
-# 透视表
-
-现有销售记录表
-
-```mysql
-create table sales(
-    id serial primary key ,
-    sku_id integer not null ,
-    amount decimal(12, 4),
-    created_at timestamp default now()
-);
-create index idx_created_at on sales(created_at);
-```
-
-现在我们希望对这个表做一个月度的透视汇总，得到2021年每个月每种商品(sku_id)的的销售总额，每个月一列，哪一项可以实现？
-
-## 答案
-
-```mysql
-select sku_id, 
-       sum(case extract(month from created_at) when 1 then amount else 0 end) as Jan,
-       sum(case extract(month from created_at) when 2 then amount else 0 end) as Feb,
-       sum(case extract(month from created_at) when 3 then amount else 0 end) as Mar,
-       sum(case extract(month from created_at) when 4 then amount else 0 end) as Apr,
-       sum(case extract(month from created_at) when 5 then amount else 0 end) as May,
-       sum(case extract(month from created_at) when 6 then amount else 0 end) as June,
-       sum(case extract(month from created_at) when 7 then amount else 0 end) as July,
-       sum(case extract(month from created_at) when 8 then amount else 0 end) as Aug,
-       sum(case extract(month from created_at) when 9 then amount else 0 end) as Sept,
-       sum(case extract(month from created_at) when 10 then amount else 0 end) as Oct,
-       sum(case extract(month from created_at) when 11 then amount else 0 end) as Nov,
-       sum(case extract(month from created_at) when 12 then amount else 0 end) as Dec
-from sales
-where created_at between '2020-01-01'::timestamp and '2021-01-01'::timestamp
-group by sku_id; 
-```
-
-## 选项
-
-### 格式不相符
-
-```mysql
-select sku_id, extract(month from created_at) as month, sum(amount) 
-from sales
-where created_at between '2020-01-01'::timestamp and '2021-01-01'::timestamp
-group by 1, 2; 
-```
-
-### 计算逻辑错误
-
-```mysql
-select sku_id, 
-       sum(amount) as Jan,
-       sum(amount) as Feb,
-       sum(amount) as Mar,
-       sum(amount) as Apr,
-       sum(amount) as May,
-       sum(amount) as June,
-       sum(amount) as July,
-       sum(amount) as Aug,
-       sum(amount) as Sept,
-       sum(amount) as Oct,
-       sum(amount) as Nov,
-       sum(amount) as Dec
-from sales
-where created_at between '2020-01-01'::timestamp and '2021-01-01'::timestamp
-group by sku_id, extract(month from created_at); 
-```
-
-### 计算格式错误
-
-```mysql
-select sku_id, 
-       sum(amount having extract(month from created_at) = 1) as Jan,
-       sum(amount having extract(month from created_at) = 2) as Feb,
-       sum(amount having extract(month from created_at) = 3) as Mar,
-       sum(amount having extract(month from created_at) = 4) as Apr,
-       sum(amount having extract(month from created_at) = 5) as May,
-       sum(amount having extract(month from created_at) = 6) as June,
-       sum(amount having extract(month from created_at) = 7) as July,
-       sum(amount having extract(month from created_at) = 8) as Aug,
-       sum(amount having extract(month from created_at) = 9) as Sept,
-       sum(amount having extract(month from created_at) = 10) as Oct,
-       sum(amount having extract(month from created_at) = 11) as Nov,
-       sum(amount having extract(month from created_at) = 12) as Dec
-from sales
-where created_at between '2020-01-01'::timestamp and '2021-01-01'::timestamp
-group by sku_id, extract(month from created_at); 
-```
\ No newline at end of file
diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/config.json" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/config.json"
index 035409fef84a44857137de1c01e348ec7f1421bc..fa37a4d2a698d69c232da877bebb2e90d436ae98 100644
--- "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/config.json"	
+++ "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/config.json"	
@@ -1,9 +1,11 @@
 {
   "node_id": "mysql-b57b6c08f5f240c6a997284e4448f088",
-  "keywords": [],
+  "keywords": ["union"],
   "children": [],
-  "export": [],
+  "export": [
+    "union.json"
+  ],
   "keywords_must": [],
   "keywords_forbid": [],
-  "group": 0
+  "group": 1
 }
\ No newline at end of file
diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/union.json" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/union.json"
new file mode 100644
index 0000000000000000000000000000000000000000..b71330f7f4380a3e215b34936ded3e8f3e9d0d9c
--- /dev/null
+++ "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/union.json"	
@@ -0,0 +1,7 @@
+{
+  "type": "code_options",
+  "author": "ccat",
+  "source": "union.md",
+  "notebook_enable": false,
+  "exercise_id": "331f369b150340f9989ccea8abfcd42f"
+}
\ No newline at end of file
diff --git "a/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/union.md" "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/union.md"
new file mode 100644
index 0000000000000000000000000000000000000000..1028f3b9176ba3ae9b6041f381bb0cb766933eb3
--- /dev/null
+++ "b/data/2.MySQL\344\270\255\351\230\266/2. \346\237\245\350\257\242/6.UNION/union.md"	
@@ -0,0 +1,77 @@
+# Union
+
+现有员工信息表和顾客信息表如下
+
+```mysql
+create table employee(
+    id int primary key auto_increment,
+    name varchar(256),
+    address varchar(1024),
+    dept varchar(64)
+    -- ignore more
+);
+
+create table customer(
+                         id int primary key auto_increment,
+                         name varchar(256),
+                         address varchar(1024),
+                         level int
+    -- ignore more
+)
+
+```
+
+Joe 需要员工和顾客的联系方式（姓名+地址）清单，用于邮寄礼品。这个查询如何写？
+
+## 答案
+
+```mysql
+select name, address 
+from customer
+union
+select name, address
+from employee
+```
+
+## 选项
+
+### A
+
+```mysql
+select * 
+from customer
+union
+select *
+from employee
+```
+
+### B
+
+```mysql
+select * 
+from customer
+join employee
+```
+
+### C
+
+```mysql
+select * 
+from customer
+join employee on customer.id = employee.id
+```
+
+### D
+
+```mysql
+select * 
+from customer, employee
+```
+
+### E
+
+```mysql
+select name, address 
+from customer, employee
+```
+