Question

This question is an extension from another question of mine @ Need some advice and feedback on coding a many:many relationship in MySQL…

I have the following MySQL code for the tables:

DROP TABLE IF EXISTS `person` ;
CREATE TABLE `person` (
  `personID` INT(5) NOT NULL AUTO_INCREMENT ,
  `firstName` VARCHAR(50) NOT NULL ,
  `lastName` VARCHAR(50) NOT NULL ,
  `dateOfBirth` DATE NOT NULL ,
  `personType` CHAR(6) NOT NULL, 
  `photo` BLOB NULL DEFAULT NULL ,
  PRIMARY KEY (`personID`))
ENGINE = InnoDB;
SHOW WARNINGS;

DROP TABLE IF EXISTS `parent` ;
CREATE TABLE `parent` (
  `parentID` INT(5) NOT NULL,
  PRIMARY KEY (`parentID`), 
  FOREIGN KEY (`parentID`) REFERENCES `person` (`personID`) 
  ON DELETE CASCADE 
  ON UPDATE CASCADE)
ENGINE = InnoDB;
SHOW WARNINGS;

DROP TABLE IF EXISTS `player` ;
CREATE TABLE Player (
    `playerID` INT(5) NOT NULL,
    `motherID` INT(5),
    `fatherID` INT(5),
    `schoolID` INT(5),
    PRIMARY KEY (`playerID`), 
    FOREIGN KEY (`playerID`) REFERENCES `person` (`personID`) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE,
    FOREIGN KEY (`motherID`) REFERENCES `parent` (`parentID`) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE,
    FOREIGN KEY (`fatherID`) REFERENCES `parent` (`parentID`) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE, 
    FOREIGN KEY (`schoolID`) REFERENCES `school` (`schoolID`) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE)
ENGINE = InnoDB;
SHOW WARNINGS;

I am wanting to format a query such that it would return information like so:

+----------+-----------------+----------------+-----------------+----------------+
| ParentID | ParentFirstName | ParentLastName | PlayerFirstName | PlayerLastName |
+----------+-----------------+----------------+-----------------+----------------+
|        1 | John            | Doe            | Maggie          | Doe            |
|        1 | John            | Doe            | Rob             | Doe            |
|        2 | Jane            | Doe            | Rob             | Doe            |
|        2 | Jane            | Doe            | Maggie          | Doe            |
|        3 | Peter           | Smith          | Neil            | Smith          |
|        3 | Peter           | Smith          | Chad            | Smith          |
|        4 | Mary            | Mason          | Neil            | Smith          |
|        4 | Mary            | Mason          | Chad            | Smith          |
+----------+-----------------+----------------+-----------------+----------------+

I notice that names are repeated several times in the above visualization, I’m also wondering if using GROUP_CONCAT would be a good idea to merge them together somehow.

I am having trouble joining these three tables in such a way to generate the query needed. Some inspiration I found (courtesy of a user on here) was found at http://sqlfiddle.com/#!2/baf8d, however I’m having trouble customising this to suit my own needs (in the example the first and last names are in each parent/player table, whereas I inherit these fields from the Person superclass.

The code below was the closest I got before deciding to ask the question on here. I thought somehow if I could merge these queries together to match something like the results above, but I got stuck with it…

mysql> select person.firstName as ParentFirstName, person.lastName as ParentLastName from person where
    -> person.personID IN (select * from parent);
+-----------------+----------------+
| ParentFirstName | ParentLastName |
+-----------------+----------------+
| John            | Doe            |
| Jane            | Doe            |
| Peter           | Smith          |
| Mary            | Mason          |
+-----------------+----------------+

mysql> select person.firstName as ChildFirstName, person.lastName as ChildLastName from person where
    -> person.personID IN (select player.playerID from player);
+----------------+---------------+
| ChildFirstName | ChildLastName |
+----------------+---------------+
| Maggie         | Doe           |
| Rob            | Doe           |
| Neil           | Smith         |
| Chad           | Smith         |
+----------------+---------------+

I felt that having the Person superclass in my database schema was necessary (as the player/parent and other “people” entities would have similar details) and its something I would rather leave in. If you are able to help me get unstuck with this problem I would appreciate it very much.

Thanks in advance!!

Answer 1

For the exact output you show, you want to join the tables as follows:

SELECT
        parent.parentID  AS ParentID,
  ParentPerson.firstName AS ParentFirstName,
  ParentPerson.lastName  AS  ParentLastName,
   ChildPerson.firstName AS PlayerFirstName,
   ChildPerson.lastName  AS  PlayerLastName
FROM
       parent
  JOIN Player ON (parent.parentID IN (Player.motherID, Player.fatherID))
  JOIN person AS ParentPerson ON (ParentPerson.personID = parent.parentID)
  JOIN person AS  ChildPerson ON ( ChildPerson.personID = Player.playerID)