add join

data/3.OceanBase高阶/3.编程和查询/2.连接查询/show_title.json

+{
+  "type": "code_options",
+  "author": "刘鑫",
+  "source": "show_title.md"
+}
\ No newline at end of file

data/3.OceanBase高阶/3.编程和查询/2.连接查询/show_title.md

+# 显示分类标题
+
+假设员工表employee和部门表department中有如下列：
+
+```sql
+create table employee(
+    id integer auto_increment primary key ,
+    name varchar(256),
+    dept int
+);
+
+create table department(
+    id integer auto_increment primary key ,
+    name varchar(256)
+)
+```
+
+员工表的 dept 列引用 department 表的主键。
+
+那么能够显示员工列表，并展示其所在部门的名称的是：
+
+## 答案
+
+```sql
+select e.id, e.name, d.name as department 
+from employee as e join department as d on e.dept = d.id
+```
+
+## 选项
+
+### 表名引用错误
+
+```sql
+select e.id, e.name, d.name as department 
+from employee as e join department as d on e.dept = d.id
+```
+
+### 连接条件错误
+
+```sql
+select e.id, e.name, e.name as department 
+from employee as e join department as d on e.id = d.id
+```
+
+### 连接条件错误
+
+```sql
+select e.id, e.name, e.name as department 
+from employee as e join department as d on e.department in d.id
+```
+
+
+### 列名存在歧义问题
+
+```sql
+select e.id, name, d.name as department 
+from employee as e join department as d on e.dept = d.id
+```