常见通用的 JOIN 查询

SQL执行循序：

手写：

SELECT DISTINCT <query_list> FROM <left_table>
<join type> JOIN <right_table> ON <join_condition>
WHERE <wherer_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
ORDER BY <order_by_list>
LIMIT <limit number>

机读：

FROM <left_table>
ON <join_condition>
<join_type> JOIN <right_table>
WHERE <where_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
SELECT
DISTINCT <query_list>
ORDER BY <order_by_condition>
LIMIT <limit_number>

总结：

理论图谱：

MySQL数据库实例：

1.创建数据库：

mysql> create database db_test;
Query OK, 1 row affected (0.01 sec)

 2.使用数据库：

mysql> use db_test;
Database changed

3.创建表、添加数据：

CREATE TABLE `tb_dept` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '部门主键',
  `deptName` varchar(30) DEFAULT NULL COMMENT '部门名称',
  `locAdd` varchar(40) DEFAULT NULL COMMENT '楼层',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

CREATE TABLE `tb_emp` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '员工主键',
  `name` varchar(20) DEFAULT NULL COMMENT '员工姓名',
  `deptId` int(11) DEFAULT NULL COMMENT '部门外键',
  PRIMARY KEY (`id`),
  KEY `fk_dept_id` (`deptId`)
  #CONSTRAINT `fk_dept_id` FOREIGN KEY (`deptId`) REFERENCES `tb_dept` (`id`) COMMENT '部门外键设置, 已经注释掉。'
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

INSERT INTO `tb_dept` VALUES ('', 'RD', '');
INSERT INTO `tb_dept` VALUES ('', 'HR', '');
INSERT INTO `tb_dept` VALUES ('', 'MK', '');
INSERT INTO `tb_dept` VALUES ('', 'MIS', '');
INSERT INTO `tb_dept` VALUES ('', 'FD', '');

INSERT INTO `tb_emp` VALUES ('', '张三', '');
INSERT INTO `tb_emp` VALUES ('', '李四', '');
INSERT INTO `tb_emp` VALUES ('', '王二', '');
INSERT INTO `tb_emp` VALUES ('', '麻子', '');
INSERT INTO `tb_emp` VALUES ('', '小马', '');
INSERT INTO `tb_emp` VALUES ('', '马旭', '');
INSERT INTO `tb_emp` VALUES ('', '小丁', '');
INSERT INTO `tb_emp` VALUES ('', '小西', '');

tb_emp表数据：

mysql> select * from tb_emp;
+----+--------+--------+
| id | name   | deptId |
+----+--------+--------+
|  1 | 张三   |      1 |
|  2 | 李四   |      1 |
|  3 | 王二   |      1 |
|  4 | 麻子   |      2 |
|  5 | 小马   |      2 |
|  6 | 马旭   |      3 |
|  7 | 小丁   |      4 |
|  8 | 小西   |     51 |
+----+--------+--------+
8 rows in set (0.01 sec)

tb_dept表数据：

mysql> select * from tb_dept;
+----+----------+--------+
| id | deptName | locAdd |
+----+----------+--------+
|  1 | RD       | 11     |
|  2 | HR       | 12     |
|  3 | MK       | 13     |
|  4 | MIS      | 14     |
|  5 | FD       | 15     |
+----+----------+--------+
5 rows in set (0.01 sec)

笛卡儿积：

mysql> select * from tb_emp, tb_dept;
+----+--------+--------+----+----------+--------+
| id | name   | deptId | id | deptName | locAdd |
+----+--------+--------+----+----------+--------+
|  1 | 张三   |      1 |  1 | RD       | 11     |
|  1 | 张三   |      1 |  2 | HR       | 12     |
|  1 | 张三   |      1 |  3 | MK       | 13     |
|  1 | 张三   |      1 |  4 | MIS      | 14     |
|  1 | 张三   |      1 |  5 | FD       | 15     |
|  2 | 李四   |      1 |  1 | RD       | 11     |
|  2 | 李四   |      1 |  2 | HR       | 12     |
|  2 | 李四   |      1 |  3 | MK       | 13     |
|  2 | 李四   |      1 |  4 | MIS      | 14     |
|  2 | 李四   |      1 |  5 | FD       | 15     |
|  3 | 王二   |      1 |  1 | RD       | 11     |
|  3 | 王二   |      1 |  2 | HR       | 12     |
|  3 | 王二   |      1 |  3 | MK       | 13     |
|  3 | 王二   |      1 |  4 | MIS      | 14     |
|  3 | 王二   |      1 |  5 | FD       | 15     |
|  4 | 麻子   |      2 |  1 | RD       | 11     |
|  4 | 麻子   |      2 |  2 | HR       | 12     |
|  4 | 麻子   |      2 |  3 | MK       | 13     |
|  4 | 麻子   |      2 |  4 | MIS      | 14     |
|  4 | 麻子   |      2 |  5 | FD       | 15     |
|  5 | 小马   |      2 |  1 | RD       | 11     |
|  5 | 小马   |      2 |  2 | HR       | 12     |
|  5 | 小马   |      2 |  3 | MK       | 13     |
|  5 | 小马   |      2 |  4 | MIS      | 14     |
|  5 | 小马   |      2 |  5 | FD       | 15     |
|  6 | 马旭   |      3 |  1 | RD       | 11     |
|  6 | 马旭   |      3 |  2 | HR       | 12     |
|  6 | 马旭   |      3 |  3 | MK       | 13     |
|  6 | 马旭   |      3 |  4 | MIS      | 14     |
|  6 | 马旭   |      3 |  5 | FD       | 15     |
|  7 | 小丁   |      4 |  1 | RD       | 11     |
|  7 | 小丁   |      4 |  2 | HR       | 12     |
|  7 | 小丁   |      4 |  3 | MK       | 13     |
|  7 | 小丁   |      4 |  4 | MIS      | 14     |
|  7 | 小丁   |      4 |  5 | FD       | 15     |
|  8 | 小西   |     51 |  1 | RD       | 11     |
|  8 | 小西   |     51 |  2 | HR       | 12     |
|  8 | 小西   |     51 |  3 | MK       | 13     |
|  8 | 小西   |     51 |  4 | MIS      | 14     |
|  8 | 小西   |     51 |  5 | FD       | 15     |
+----+--------+--------+----+----------+--------+
40 rows in set (0.00 sec)

查询tb_emp表和tb_dept中公共的数据：

mysql> select * from tb_emp e
    -> inner join tb_dept d on e.deptId = d.id;
+----+--------+--------+----+----------+--------+
| id | name   | deptId | id | deptName | locAdd |
+----+--------+--------+----+----------+--------+
|  1 | 张三   |      1 |  1 | RD       | 11     |
|  2 | 李四   |      1 |  1 | RD       | 11     |
|  3 | 王二   |      1 |  1 | RD       | 11     |
|  4 | 麻子   |      2 |  2 | HR       | 12     |
|  5 | 小马   |      2 |  2 | HR       | 12     |
|  6 | 马旭   |      3 |  3 | MK       | 13     |
|  7 | 小丁   |      4 |  4 | MIS      | 14     |
+----+--------+--------+----+----------+--------+
7 rows in set (0.00 sec)

查询tb_emp表中全部的数据：

mysql> select * from tb_emp e
    -> left join tb_dept d on e.deptId = d.id;
+----+--------+--------+------+----------+--------+
| id | name   | deptId | id   | deptName | locAdd |
+----+--------+--------+------+----------+--------+
|  1 | 张三   |      1 |    1 | RD       | 11     |
|  2 | 李四   |      1 |    1 | RD       | 11     |
|  3 | 王二   |      1 |    1 | RD       | 11     |
|  4 | 麻子   |      2 |    2 | HR       | 12     |
|  5 | 小马   |      2 |    2 | HR       | 12     |
|  6 | 马旭   |      3 |    3 | MK       | 13     |
|  7 | 小丁   |      4 |    4 | MIS      | 14     |
|  8 | 小西   |     51 | NULL | NULL     | NULL   |　　　　#该条数据为 tb_emp 表中独有的数据, tb_dept 表中的字段用 null 占位
+----+--------+--------+------+----------+--------+
8 rows in set (0.00 sec)

查询tb_dept表中全部的数据：

mysql> select * from tb_emp e
    -> right join tb_dept d on e.deptId = d.id;
+------+--------+--------+----+----------+--------+
| id   | name   | deptId | id | deptName | locAdd |
+------+--------+--------+----+----------+--------+
|    1 | 张三   |      1 |  1 | RD       | 11     |
|    2 | 李四   |      1 |  1 | RD       | 11     |
|    3 | 王二   |      1 |  1 | RD       | 11     |
|    4 | 麻子   |      2 |  2 | HR       | 12     |
|    5 | 小马   |      2 |  2 | HR       | 12     |
|    6 | 马旭   |      3 |  3 | MK       | 13     |
|    7 | 小丁   |      4 |  4 | MIS      | 14     |
| NULL | NULL   |   NULL |  5 | FD       | 15     |     #该条数据为 tb_dept 表中独有的数据, tb_emp 表中的字段用 null 占位
+------+--------+--------+----+----------+--------+
8 rows in set (0.01 sec)

查询tb_emp表中独有的数据：

mysql> select * from tb_emp e
    -> left join tb_dept d on e.deptId = d.id
    -> where d.id is null;
+----+--------+--------+------+----------+--------+
| id | name   | deptId | id   | deptName | locAdd |
+----+--------+--------+------+----------+--------+
|  8 | 小西   |     51 | NULL | NULL     | NULL   |
+----+--------+--------+------+----------+--------+
1 row in set (0.00 sec)

查询tb_dept表中独有的数据：

mysql> select * from tb_emp e
    -> right join tb_dept d on e.deptId = d.id
    -> where e.deptId is null;
+------+------+--------+----+----------+--------+
| id   | name | deptId | id | deptName | locAdd |
+------+------+--------+----+----------+--------+
| NULL | NULL |   NULL |  5 | FD       | 15     |
+------+------+--------+----+----------+--------+
1 row in set (0.00 sec)

查询tb_emp和tb_dept表中所有的数据：

mysql> select * from tb_emp e
    -> full outer join tb_dept d on e.deptId = d.id;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'full outer join tb_dept d on e.deptId = d.id' at line 2

出错原因：mysql 中不支持这种连接方式。

解决办法：左连接数据和右连接数据相加，将公共的部分去重。

mysql> select * from tb_emp e
    -> left join tb_dept d on e.deptId = d.id
    -> union　　　　　#去重
    -> select * from tb_emp e
    -> right join tb_dept d on e.deptId = d.id;
+------+--------+--------+------+----------+--------+
| id   | name   | deptId | id   | deptName | locAdd |
+------+--------+--------+------+----------+--------+
|    1 | 张三   |      1 |    1 | RD       | 11     |
|    2 | 李四   |      1 |    1 | RD       | 11     |
|    3 | 王二   |      1 |    1 | RD       | 11     |
|    4 | 麻子   |      2 |    2 | HR       | 12     |
|    5 | 小马   |      2 |    2 | HR       | 12     |
|    6 | 马旭   |      3 |    3 | MK       | 13     |
|    7 | 小丁   |      4 |    4 | MIS      | 14     |
|    8 | 小西   |     51 | NULL | NULL     | NULL   |　　　　#该条数据为 tb_emp 表中独有的数据, tb_dept 表中的字段用 null 占位
| NULL | NULL   |   NULL |    5 | FD       | 15     |　　　 #该条数据为 tb_dept 表中独有的数据, tb_emp 表中的字段用 null 占位
+------+--------+--------+------+----------+--------+
9 rows in set (0.00 sec)

查询tb_emp和tb_dept表中独有的数据：

mysql> select * from tb_emp e
    -> left join tb_dept d on e.deptId = d.id
    -> where d.id is null
    -> union
    -> select * from tb_emp e
    -> right join tb_dept d on e.deptId = d.id
    -> where e.deptId is null;
+------+--------+--------+------+----------+--------+
| id   | name   | deptId | id   | deptName | locAdd |
+------+--------+--------+------+----------+--------+
|    8 | 小西   |     51 | NULL | NULL     | NULL   |
| NULL | NULL   |   NULL |    5 | FD       | 15     |
+------+--------+--------+------+----------+--------+
2 rows in set (0.00 sec)