Question

I’m having a problem with logic programming, but I think that could be another solution much easier to do this in a SQL command, however, let’s go to the problem.

I have a table in MySQL (InnoDb) like this:

CREATE TABLE IF NOT EXISTS `folder` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `folder_id` INT NOT NULL ,
  `name` VARCHAR(100) NULL ,
  `hidden` TINYINT(1)  NOT NULL DEFAULT 0 ,
  PRIMARY KEY (`id`) ,
  INDEX `fk_folder_folder1` (`folder_id` ASC) ,
  CONSTRAINT `fk_folder_folder1`
    FOREIGN KEY (`folder_id` )
    REFERENCES `folder` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB

It seems like a pretty simple, but I want to list the folders, in a way that the subfolders of this folder will appear below it. Like in any file repository.

For example:
In the table:

id  name    folder_id
1   root    1
2   etc     1
3   dev     1
4   apache  2
5   php     2
6   mysql   2
7   hda     3
8   hda1    3
9   lib     1

I want to show it like this:

root
    etc
        apache
        php
        mysql
    dev
        hda
        hda1
    lib

The question is, have a way to do this by SQL command or in PHP?

I try make in PHP, and I don’t see a way without a recursive function. But i haven’t success.

Solution:
Because the MySQL doesn’t accept the WITH clause, the recursive function in SQL is out of the box. Thanks guys.

SELECT c2.name
FROM folder c1 LEFT OUTER JOIN folder c2
ON c2.folder_id = c1.id WHERE c2.folder_id = 1  // the id of the parent folder
AND c2.id != c2.folder_id               // Remove the parent folder
ORDER BY c2.folder ASC

Answer 1

you’re in danger of implementing an SQL anti pattern called naive trees.
See the pdf of the book, it shows several good solutions.