mysql 连接查询
作者:互联网
连接语法
select 字段
from 表名1,表名2
where 表名1.key = 表名2.key
[group by 字段]
[having 条件]
[order by 字段 [desc|asc]]
select 字段...
from 表名1
【连接类型】join 表名2 on 表名1.key = 表名2.key
[where 条件]
[group by 条件]
[having 条件]
[order by 字段 [desc|asc]
等值连接
查询学生id,名字,班级名称 方法一:
SELECT
student.id,
student.name student_name,
class.name class_name
FROM
student,
class
WHERE
student.class_id = class.id;
+----+--------------+------------+
| id | student_name | class_name |
+----+--------------+------------+
| 1 | 张三 | 班级1 |
| 2 | 王五 | 班级1 |
| 3 | 李四 | 班级1 |
| 4 | 小红 | 班级2 |
| 5 | 小花 | 班级2 |
| 6 | huyongjian | 班级3 |
| 7 | Join | 班级3 |
+----+--------------+------------+
方法二:
SELECT
student.id,
student.name student_name,
class.name class_name
FROM
student
INNER JOIN class ON student.class_id = class.id;
+----+--------------+------------+
| id | student_name | class_name |
+----+--------------+------------+
| 1 | 张三 | 班级1 |
| 2 | 王五 | 班级1 |
| 3 | 李四 | 班级1 |
| 4 | 小红 | 班级2 |
| 5 | 小花 | 班级2 |
| 6 | huyongjian | 班级3 |
| 7 | Join | 班级3 |
+----+--------------+------------+
左连接
SELECT
student.`id`,
student.`name` student_name,
class.`name` class_name
FROM
student
LEFT JOIN class ON student.`class_id` = class.`id`;
+----+--------------+------------+
| id | student_name | class_name |
+----+--------------+------------+
| 1 | 张三 | 班级1 |
| 2 | 王五 | 班级1 |
| 3 | 李四 | 班级1 |
| 4 | 小红 | 班级2 |
| 5 | 小花 | 班级2 |
| 6 | huyongjian | 班级3 |
| 7 | Join | NULL |
+----+--------------+------------+
7 rows in set (0.00 sec)
右连接
SELECT
student.`id`,
student.`name` student_name,
class.`name` class_name
FROM
student
RIGHT JOIN class ON student.`class_id` = class.`id`;
+------+--------------+------------+
| id | student_name | class_name |
+------+--------------+------------+
| 3 | 李四 | 班级1 |
| 2 | 王五 | 班级1 |
| 1 | 张三 | 班级1 |
| 7 | Join | 班级2 |
| 6 | huyongjian | 班级2 |
| 5 | 小花 | 班级2 |
| 4 | 小红 | 班级2 |
| NULL | NULL | 班级3 |
+------+--------------+------------+
8 rows in set (0.00 sec)
标签:班级,name,连接,查询,+----+--------------+------------+,student,mysql,id,class 来源: https://www.cnblogs.com/hu308830232/p/14993131.html