MySQL: Tree-Hierarchical query

Question

SUB-TREE WITHIN A TREE in MySQL

In my MYSQL Database COMPANY, I have a Table: Employee with recursive association, an employee can be boss of other employee. A self relationship of kind (SuperVisor (1)- SuperVisee (∞) ).

Query to Create Table:

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;

I have inserted a set of tuples (Query):

INSERT INTO Employee VALUES 
 ("1", "A", "OWNER",  "1"),  

 ("2", "B", "BOSS",   "1"), # Employees under OWNER 
 ("3", "F", "BOSS",   "1"),

 ("4", "C", "BOSS",   "2"), # Employees under B
 ("5", "H", "BOSS",   "2"), 
 ("6", "L", "WORKER", "2"), 
 ("7", "I", "BOSS",   "2"), 
 # Remaining Leaf nodes   
 ("8", "K", "WORKER", "3"), # Employee under F     

 ("9", "J", "WORKER", "7"), # Employee under I     

 ("10","G", "WORKER", "5"), # Employee under H

 ("11","D", "WORKER", "4"), # Employee under C
 ("12","E", "WORKER", "4")  

The inserted rows has following Tree-Hierarchical-Relationship:

         A     <---ROOT-OWNER
        /|\             
       / A \        
      B     F 
    //| \    \          
   // |  \    K     
  / | |   \                     
 I  L H    C        
/     |   / \ 
J     G  D   E

I written a query to find relationship:

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;

And output is:

+------------+------------+----------+
| SuperVisor | SuperVisee | COUNT(*) |
+------------+------------+----------+
| A          | A,B,F      |        3 |
| B          | C,H,I,L    |        4 |
| C          | D,E        |        2 |
| F          | K          |        1 |
| H          | G          |        1 |
| I          | J          |        1 |
+------------+------------+----------+
6 rows in set (0.00 sec)

[QUESTION]
Instead of complete Hierarchical Tree, I need a SUB-TREE from a point (selective) e.g.:
If input argument is B then output should be as below...

+------------+------------+----------+
| SuperVisor | SuperVisee | COUNT(*) |
+------------+------------+----------+
| B          | C,H,I,L    |        4 |
| C          | D,E        |        2 |
| H          | G          |        1 |
| I          | J          |        1 |
+------------+------------+----------+   

Please help me on this. If not query, a stored-procedure can be helpful.
I tried, but all efforts were useless!

Answer 1

I already addressed something of this nature using Stored Procedures : Find highest level of a hierarchical field: with vs without CTEs (Oct 24, 2011)

If you look in my post, you could use the GetAncestry and GetFamilyTree functions as a model for traversing the tree from any given point.

UPDATE 2012-12-11 12:11 EDT

I looked back at my code from my post. I wrote up the Stored Function for you:

DELIMITER $$
DROP FUNCTION IF EXISTS cte_test.GetFamilyTree $$
CREATE FUNCTION cte_test.GetFamilyTree(GivenName varchar(64))
RETURNS varchar(1024) CHARSET latin1
DETERMINISTIC
BEGIN
DECLARE rv,q,queue,queue_children,queue_names VARCHAR(1024);
DECLARE queue_length,pos INT;
DECLARE GivenSSN,front_ssn VARCHAR(64);

SET rv = '';

SELECT SSN INTO GivenSSN
FROM Employee
WHERE name = GivenName
AND Designation <> 'OWNER';
IF ISNULL(GivenSSN) THEN
    RETURN ev;
END IF;

SET queue = GivenSSN;
SET queue_length = 1;

WHILE queue_length > 0 DO
    IF queue_length = 1 THEN
        SET front_ssn = queue;
        SET queue = '';
    ELSE
        SET pos = LOCATE(',',queue);
        SET front_ssn = LEFT(queue,pos - 1);
        SET q = SUBSTR(queue,pos + 1);
        SET queue = q;
    END IF;
    SET queue_length = queue_length - 1;
    SELECT IFNULL(qc,'') INTO queue_children
    FROM
    (
        SELECT GROUP_CONCAT(SSN) qc FROM Employee
        WHERE MSSN = front_ssn AND Designation <> 'OWNER'
    ) A;
    SELECT IFNULL(qc,'') INTO queue_names
    FROM
    (
        SELECT GROUP_CONCAT(name) qc FROM Employee
        WHERE MSSN = front_ssn AND Designation <> 'OWNER'
    ) A;
    IF LENGTH(queue_children) = 0 THEN
        IF LENGTH(queue) = 0 THEN
            SET queue_length = 0;
        END IF;
    ELSE
        IF LENGTH(rv) = 0 THEN
            SET rv = queue_names;
        ELSE
            SET rv = CONCAT(rv,',',queue_names);
        END IF;
        IF LENGTH(queue) = 0 THEN
            SET queue = queue_children;
        ELSE
            SET queue = CONCAT(queue,',',queue_children);
        END IF;
        SET queue_length = LENGTH(queue) - LENGTH(REPLACE(queue,',','')) + 1;
    END IF;
END WHILE;

RETURN rv;


END $$

It actually works. Here is a sample:

mysql> SELECT name,GetFamilyTree(name) FamilyTree
    -> FROM Employee WHERE Designation <> 'OWNER';
+------+-----------------------+
| name | FamilyTree            |
+------+-----------------------+
| A    | B,F,C,H,L,I,K,D,E,G,J |
| G    |                       |
| D    |                       |
| E    |                       |
| B    | C,H,L,I,D,E,G,J       |
| F    | K                     |
| C    | D,E                   |
| H    | G                     |
| L    |                       |
| I    | J                     |
| K    |                       |
| J    |                       |
+------+-----------------------+
12 rows in set (0.36 sec)
mysql>

There is only one catch. I added one extra row for the owner

• The owner has SSN 0
• The owner is his own boss with MSSN 0

Here is the data

mysql> select * from Employee;
+-----+------+-------------+------+
| SSN | Name | Designation | MSSN |
+-----+------+-------------+------+
| 0   | A    | OWNER       | 0    |
| 1   | A    | BOSS        | 0    |
| 10  | G    | WORKER      | 5    |
| 11  | D    | WORKER      | 4    |
| 12  | E    | WORKER      | 4    |
| 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    |
+-----+------+-------------+------+
13 rows in set (0.00 sec)
mysql>

Answer 2

What you are using is called Adjacency List Model. It has a lot of limitations. You'll be problem when you want to delete/insert a node at a specific place. Its better you use Nested Set Model.

There is a detailed explanation. Unfortunately the article on mysql.com is does not exist any more.