GROUP_CONCAT with ORDER BY , but results are not orderd - mysql

Question

SELECT
*,
(SELECT
GROUP_CONCAT(url SEPARATOR '$$' )
FROM project_photos
WHERE project_id = projects.id
ORDER BY priority) AS images
FROM projects
WHERE catID = 2
LIMIT 0,5
above query works fine but the images coloumn are not ordered as priority , unable to understand why it is happening
// Structure for table project is
CREATE TABLE `projects` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`catID` int(11) NOT NULL,
`title` varchar(255) NOT NULL,
`description` varchar(400) NOT NULL,
`url` varchar(255) DEFAULT NULL,
`tags` varchar(255) DEFAULT NULL,
`featured` varchar(3) NOT NULL DEFAULT 'No',
`featured_url` varchar(255) DEFAULT NULL,
`order` int(11) DEFAULT NULL,
`created_at` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
KEY `catID` (`catID`),
CONSTRAINT `FK_catID` FOREIGN KEY (`catID`) REFERENCES `category` (`catID`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=48 DEFAULT CHARSET=latin1;
// Structure for table project_photos is
CREATE TABLE `project_photos` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`url` varchar(250) DEFAULT NULL,
`project_id` int(11) DEFAULT NULL,
`priority` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=347 DEFAULT CHARSET=utf8;

Answer 1

Ordering using ORDER BY is done after applying aggregate functions like GROUP_CONCAT(). To sort the result of GROUP_CONCAT() put it inside the argument:
SELECT
GROUP_CONCAT(url ORDER BY priority SEPARATOR '$$')
FROM project_photos
WHERE project_id = projects.id

Answer 2

Try use ORDER BY inside the GROUP_CONCAT
SELECT
*,
(SELECT
GROUP_CONCAT(url ORDER BY priority SEPARATOR '$$' )
FROM project_photos
WHERE project_id = projects.id
) AS images
FROM projects
WHERE catID = 2
LIMIT 0,5

Answer 3

You should put the order by clause inside the group concat :
GROUP_CONCAT(url SEPARATOR '$$' ORDER BY priority)
The order by outside is ordering the different rows. Since you have only one, it does nothing. Inside the group concat, it will order the elements of the group created by the group by clause.