MySQL学习3--联表查询

mysql> select * from dept;
+----+-----------+
| id | deptName  |
+----+-----------+
|  3 | 教学部    |
+----+-----------+
1 row in set (0.00 sec)

mysql> select * from employee;
+----+---------+--------+---------------------+
| id | empName | deptId | regTime             |
+----+---------+--------+---------------------+
|  1 | 老邢    |      3 | 2023-06-29 16:28:09 |
|  4 | 老万    |      3 | 2023-06-29 16:28:47 |
|  5 | 小磊    |      3 | 2023-06-29 16:28:48 |
+----+---------+--------+---------------------+

mysql> select employee.id, employee.empName, dept.deptName  #查什么
    ->from  employee,dept #从哪查   多张表使用逗号隔开
    ->where  employee.deptId = dept.id and employee.empName = "老邢";#约束的条件一定要带

+----+---------+-----------+
| id | empName | deptName  |
+----+---------+-----------+
|  1 | 老邢    | 教学部    |
+----+---------+-----------+

mysql> select e.id, e.empName, d.deptName
    -> from employee e, dept d
    -> where e.deptId = d.id;
+----+---------+-----------+
| id | empName | deptName  |
+----+---------+-----------+
|  1 | 老邢    | 教学部    |
|  4 | 老万    | 教学部    |
|  5 | 小磊    | 教学部    |
+----+---------+-----------+

mysql> select e.id as "编号", e.empName as "名字", d.deptName as "部门"
    -> from employee e, dept d
    -> where e.deptId = d.id;
+--------+--------+-----------+
| 编号   | 名字   | 部门      |
+--------+--------+-----------+
|      1 | 老邢   | 教学部    |
|      4 | 老万   | 教学部    |
|      5 | 小磊   | 教学部    |
+--------+--------+-----------+

select 字段
from 表1
inner join 表2
on 约束关系

mysql> select d.deptName, e.empName
    -> from dept d
    -> inner join employee e
    -> on d.id = e.deptId;
+-----------+---------+
| deptName  | empName |
+-----------+---------+
| 教学部    | 老邢    |
| 教学部    | 老万    |
| 教学部    | 小磊    |
+-----------+---------+

mysql> select e.empName, d.deptName
    -> from employee e
    -> inner join dept d
    -> on e.deptId = d.id
    -> where e.empName = "老邢";
+---------+-----------+
| empName | deptName  |
+---------+-----------+
| 老邢    | 教学部    |
+---------+-----------+

select 字段 from 左表1 left outer join 右表2 on 约束条件

mysql> select d.deptName, e.empName
    -> from dept d
    -> left outer join employee e
    -> on d.id = e.deptId;
+-----------+---------+
| deptName  | empName |
+-----------+---------+
| 教学部    | 老邢    |
| 教学部    | 老万    |
| 教学部    | 小磊    |
| 技术部    | NULL    |
+-----------+---------+

select 字段  from 左表1  right outer join 右表2 on  约束条件

mysql> select *
    -> from employee e
    -> right outer join dept d
    -> on e.deptId = d.id;
+------+---------+--------+---------------------+----+-----------+
| id   | empName | deptId | regTime             | id | deptName  |
+------+---------+--------+---------------------+----+-----------+
|    1 | 老邢    |      1 | 2022-04-25 10:08:04 |  1 | 教学部    |
|    2 | 雪珂    |      2 | 2022-04-25 10:08:17 |  2 | 行政部    |
|    3 | 凯旗    |      3 | 2022-04-25 10:08:30 |  3 | 技术部    |
|    4 | 小磊    |      1 | 2022-04-25 10:08:43 |  1 | 教学部    |
|    5 | 帅栋    |      1 | 2022-04-25 10:08:56 |  1 | 教学部    |
| NULL | NULL    |   NULL | NULL                |  4 | 后勤部    |
+------+---------+--------+---------------------+----+-----------+

select ts.s_name, tt.t_name
from t_student ts
inner joint_teacher tt
on ts.teacher_id = tt.t_id
where ts.s_name = "邱博"

select tt.t_name, ts.s_name
from t_teacher tt
inner join t_student ts
on tt.t_id = ts.teacher_id
where tt.t_name = "老邢"

select tt.t_name, ts.s_name
from t_student ts, t_teacher tt
where ts.teacher_id = tt.t_id and tt.t_name = '老邢'

#看所有学生选择了哪些的课程
select ts.s_name, tc.c_name
from t_stu ts
inner join stu_course sc
on ts.s_id = sc.stu_id
inner join t_course tc
on sc.course_id = tc.c_id
#查看狗蛋选择了哪些课程
select ts.s_name, tc.c_name
from t_stu ts
inner join stu_course sc
on ts.s_id = sc.stu_id
inner join t_course tc
on sc.course_id = tc.c_id
where ts.s_name = "狗蛋"

#Java被哪些学生选择了
先写课程表
select *
from t_course tc
inner join stu_course sc
on tc.c_id = sc.course_id
inner join t_stu ts
on sc.stu_id = ts.s_id
where tc.c_name = "Java"