Question

I am trying to use two GROUP_CONCATs in the same SQL statement.

I have the following code:

try
{
$sql = 'SELECT player.id, player.name AS name, GROUP_CONCAT(previousclubs.name) 
        previousclubs, satscore, gpa, GROUP_CONCAT(link) link
            FROM player INNER JOIN playerpreviousclubs
                ON player.id = playerid
            INNER JOIN previousclubs
                    ON previousclubid = previousclubs.id
            INNER JOIN links
                ON links.playerid = player.id
            GROUP BY player.id';

$result = $pdo->query($sql);
}
catch (PDOException $e)
{
$error = 'Error fetching details: ' . $e->getMessage();
include 'error.html.php';
exit();
}

foreach ($result as $row)
{
$names[] = array(
                'id' => $row['id'], 
                'name' => $row['name'],
                'previousclubs' => $row['previousclubs'],
                'links' => $row['link']
                );
}
include 'profiles.html.php';

If a player has say three previous clubs and one link, then instead of displaying like this:

Name: John Smith

Previous Clubs: Arsenal, Reading, QPR

Links: http://www.bbc.co.uk

IT DISPLAYS LIKE THIS:

Name: John Smith

Previous Clubs: Arsenal, Reading, QPR

Links: http://www.bbc.co.uk, http://www.bbc.co.uk, http://www.bbc.co.uk

WORSE STILL IF YOU HAVE MULTIPLE LINKS (TWO LINKS ARE USED BELOW) YOU GET THIS:

Name: John Smith

Previous Clubs: Arsenal, Arsenal, Reading, Reading, QPR, QPR

Links: http://www.bbc.co.uk, http://www.football.com, http://www.bbc.co.uk, http://www.football.com, http://www.bbc.co.uk, http://www.football.com

Can someone please provide some guidance on what is going on here and how to rectify it.

The first GROUP_CONCAT on previousclubs works fine by itself but when the second GROUP_CONCAT for links is thrown in the mix, the issues mentioned above are occuring.

Thanks for your time and help.

Answer 1

The problem is not GROUP_CONCAT, it is the arguments.

Your second group concat should be:

GROUP_CONCAT(distinct link) link 

You can also control the ordering (in case you want most recent first, for instance). Check out the help page at http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat.