将不同的重复ID值合并为单行

Question

I'm developing a application for library management. The problem is, I have the following tables: user, employee, loan, book_loan, with them I need a query that returns me an unique loan's ID, with the user's name, employee's name, book's name, loan's date, devolution's date and status. I almost did this, but it returns me duplicates of the loan's ID, with the book's name separated by the rows.

These are my tables:

delimiter $$

CREATE TABLE `Loan` (
  `id_loan` int(11) NOT NULL AUTO_INCREMENT,
  `id_user` int(11) NOT NULL,
  `id_employee` int(11) NOT NULL,
  `date_loan` date NOT NULL,
  `data_devolution` date NOT NULL,
  `status` tinyint(1) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id_loan`),
  KEY `fk_loan_id_user_idx` (`id_user`),
  KEY `fk_loan_id_employee` (`id_employee`),
  CONSTRAINT `fk_loan_id_employee` FOREIGN KEY (`id_emplyee`) REFERENCES `Employee` (`id_employee`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_loan_id_user` FOREIGN KEY (`id_user`) REFERENCES `User` (`id_user`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=33 DEFAULT CHARSET=utf8$$


delimiter $$

CREATE TABLE `Employee` (
  `id_employee` int(11) NOT NULL AUTO_INCREMENT,
  `login` varchar(20) NOT NULL,
  `password` varchar(16) NOT NULL,
  `level` decimal(10,0) NOT NULL,
  PRIMARY KEY (`id_employee`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8$$


delimiter $$

CREATE TABLE `Book` (
  `id_book` int(11) NOT NULL AUTO_INCREMENT,
  `title` varchar(50) NOT NULL,
  `id_author` int(11) NOT NULL,
  `edition` decimal(10,0) NOT NULL,
  `editor` varchar(45) NOT NULL,
  `cutter` varchar(12) NOT NULL,
  `id_CDU` int(11) NOT NULL,
  `status` tinyint(1) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id_book`),
  KEY `fk_book_id_CDU_idx` (`id_CDU`),
  KEY `fk_book_id_author` (`id_author`),
  CONSTRAINT `fk_book_id_author` FOREIGN KEY (`id_author`) REFERENCES `Author` (`id_author`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_book_id_CDU` FOREIGN KEY (`id_CDU`) REFERENCES `CDU` (`id_CDU`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8$$


delimiter $$

CREATE TABLE `Book_Loan` (
  `id_book` int(11) NOT NULL,
  `id_loan` int(11) NOT NULL,
  KEY `fk_book_loan_id_loan` (`id_loan`),
  KEY `fk_book_loan_id_book` (`id_book`),
  CONSTRAINT `fk_book_loan_id_loan` FOREIGN KEY (`id_loan`) REFERENCES `Loan` (`id_loan`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_book_loan_id_book` FOREIGN KEY (`id_book`) REFERENCES `Book` (`id_book`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8$$


delimiter $$

CREATE TABLE `User` (
  `id_user` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  `address` varchar(50) NOT NULL,
  `email` varchar(50) NOT NULL,
  PRIMARY KEY (`id_user`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8$$

This is my query:

SELECT loan.id_loan AS ID,
        employee.login AS EMPLOYEE,
        user.name AS USER,
        book.title AS BOOK,
        loan.date_loan AS LOAN,
        loan.date_devolution AS DEVOLUTION,
        loan.status AS STATUS

FROM Loan loan
INNER JOIN Employee employee ON employee.id_employee = loan.id_employee
INNER JOIN User user ON user.id_user = loan.id_user
INNER JOIN Book_Loan book_loan ON book_loan.id_loan = loan.id_loan
INNER JOIN Book book ON book.id_book = book_loan.id_book;

That returns me eg: if the loan has 3 book, which is the maximum:

+-----+-------------+-------------+---------------------------------+------------+------------+--------+
| ID  | EMPLOYEE    | USER        | BOOK                            | LOAN       | DEVOLUTION| STATUS |
+-----+-------------+-------------+---------------------------------+------------+------------+--------+
|   6 | RUBE        | John        | Book A                          | 2013-06-22 | 2013-06-29 |      0 |
|   6 | RUBE        | John        | Book B                          | 2013-06-22 | 2013-06-29 |      0 |
|   6 | RUBE        | John        | Book C                          | 2013-06-22 | 2013-06-29 |      0 |
+-----+-------------+-------------+---------------------------------+------------+------------+--------+

This is what I want:

+-----+-------------+-------------+---------------------------------+------------+------------+--------+
| ID  | EMPLOYEE    | USER        | BOOK                            | LOAN       | DEVOLUTION | STATUS |
+-----+-------------+-------------+---------------------------------+------------+------------+--------+
|   6 | RUBE        | John        | Book A, Book B, Book C          | 2013-06-22 | 2013-06-29 |      0 |
+-----+-------------+-------------+---------------------------------+------------+------------+--------+

Answer 1

Look into using GROUP_CONCAT :

SELECT loan.id_loan AS ID,
        employee.login AS EMPLOYEE,
        user.name AS USER,
        GROUP_CONCAT(book.title) AS BOOK,
        loan.date_loan AS LOAN,
        loan.date_devolution AS DEVOLUTION,
        loan.status AS STATUS
FROM Loan loan
    INNER JOIN Employee employee ON employee.id_employee = loan.id_employee
    INNER JOIN User user ON user.id_user = loan.id_user
    INNER JOIN Book_Loan book_loan ON book_loan.id_loan = loan.id_loan
    INNER JOIN Book book ON book.id_book = book_loan.id_book
GROUP BY loan.id_loan