1

I have a table which having parent child relatiionship like this,

Employee_ID     |  Employee_Manager_ID   |  Employee_Name
--------------------------------------------------------
1               |  1                    |  AAAA
2               |  1                    |  BBBB
3               |  2                    |  CCCC
4               |  3                    |  DDDD
5               |  3                    |  EEEEE

Is it possible to get the count of all the employees come under a particular employee(Not only direct child,count of all the childs of child ) using a single query ?

Eg if the input  = 1
output should be 4

if input  = 2 ,output should be  3

thanks in advance

4

2 回答 2

2

假设您的表是： 

mysql> SELECT * FROM Employee;
    +-----+------+-------------+------+
    | SSN | Name | Designation | MSSN |
    +-----+------+-------------+------+
    | 1   | A    | OWNER       | 1    |
    | 10  | G    | WORKER      | 5    |
    | 11  | D    | WORKER      | 5    |
    | 12  | E    | WORKER      | 5    |
    | 2   | B    | BOSS        | 1    |
    | 3   | F    | BOSS        | 1    |
    | 4   | C    | BOSS        | 2    |
    | 5   | H    | BOSS        | 2    |
    | 6   | L    | WORKER      | 2    |
    | 7   | I    | BOSS        | 2    |
    | 8   | K    | WORKER      | 3    |
    | 9   | J    | WORKER      | 7    |
    +-----+------+-------------+------+
    12 rows in set (0.00 sec)

查询是： 

SELECT  SUPERVISOR.name AS SuperVisor, 
        GROUP_CONCAT(SUPERVISEE.name  ORDER BY SUPERVISEE.name ) AS SuperVisee, 
        COUNT(*)  
FROM Employee AS SUPERVISOR 
  INNER JOIN Employee SUPERVISEE ON  SUPERVISOR.SSN = SUPERVISEE.MSSN 
GROUP BY SuperVisor;

查询将产生如下结果：

    +------------+------------+----------+
    | SuperVisor | SuperVisee | COUNT(*) |
    +------------+------------+----------+
    | A          | A,B,F      |        3 |
    | B          | C,H,I,L    |        4 |
    | F          | K          |        1 |
    | H          | D,E,G      |        3 |
    | I          | J          |        1 |
    +------------+------------+----------+
    5 rows in set (0.00 sec)

[答案]：这对于一个级别（立即监督）要查找所有可能级别的所有监督，您必须使用 while 循环（使用存储过程）。

尽管可以检索每个级别的员工，然后获取他们的 UNION，但通常我们不能在不使用循环机制的情况下指定诸如“检索所有级别的员工的监督者”之类的查询。"

参考：在这张幻灯片中阅读幻灯片编号 23。这本书是“第四版数据库系统基础”，在“关系代数和关系微积分”一章中有一个主题“递归闭包运算”。

为创建表添加查询，可能对您有帮助： 

mysql> CREATE TABLE IF NOT EXISTS `Employee` (
    ->   `SSN` varchar(64) NOT NULL,
    ->   `Name` varchar(64) DEFAULT NULL,
    ->   `Designation` varchar(128) NOT NULL,
    ->   `MSSN` varchar(64) NOT NULL, 
    ->   PRIMARY KEY (`SSN`),
    ->   CONSTRAINT `FK_Manager_Employee`  FOREIGN KEY (`MSSN`) REFERENCES Employee(SSN)
    -> ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.17 sec)

您可以检查表，如： 

mysql> DESCRIBE Employee;
+-------------+--------------+------+-----+---------+-------+
| Field       | Type         | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| SSN         | varchar(64)  | NO   | PRI | NULL    |       |
| Name        | varchar(64)  | YES  |     | NULL    |       |
| Designation | varchar(128) | NO   |     | NULL    |       |
| MSSN        | varchar(64)  | NO   | MUL | NULL    |       |
+-------------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
于 2012-12-06T06:11:22.903 回答
0

你可以试试这个：

    SELECT
      table_name.Employee_ID,
      table_name.Employee_Name,
      COUNT(*) AS children
    FROM
      table_name AS t_one
    INNER JOIN table_name AS t_two ON
      t_two.Employee_Manager_ID=t_one.Employee_ID
    GROUP BY
      t_one.Employee_ID
于 2012-12-06T06:28:07.363 回答