Question

I like to use self explaining names for associative selects, and sometimes it’s even mandatory to avoid duplicates, so I use the AS keyword alot. But it’s giving me some trouble with left joins.

This works:

$sql = "SELECT *,
        projects.id as projects_id
       FROM projects";

$sql .= " LEFT JOIN".
    " (SELECT 
        projectfiles.id as projectfiles_id,
        projectfiles.fileID as projectfiles_fileID,
        projectfiles.projectID as projectfiles_projectID
       FROM projectfiles
       ) AS projectfiles".
    " ON projects.id = projectfiles_projectID";

However now I end up with useless data from projects, because it also picks up the fields userID and name, which I don’t need. It’s also picking up the id twice.

So I tried changing it to;

$sql = "SELECT 
        projects.id as projects_id
       FROM projects";

With the ON line becoming

" ON projects_id = projectfiles_projectID";

But that gave the error Unknown column projects_id

So I tried

" ON projects.projects_id = projectfiles_projectID";

But still the same error

I then started experimenting, and tried (as a test)

$sql = "SELECT id,name,userID FROM projects";

$sql .= " LEFT JOIN".
    " (SELECT 
        projectfiles.id as projectfiles_id,
        projectfiles.fileID as projectfiles_fileID,
        projectfiles.projectID as projectfiles_projectID
       FROM projectfiles
       ) AS projectfiles".
    " ON projects.id = projectfiles_projectID";

And to my surprise, the LEFT JOIN didn’t seem to pick up anything at all.

Code:

$sql = "SELECT id,name,userID FROM projects";

$sql .= " LEFT JOIN".
    " (SELECT 
        projectfiles.id as projectfiles_id,
        projectfiles.fileID as projectfiles_fileID,
        projectfiles.projectID as projectfiles_projectID
       FROM projectfiles
       ) AS projectfiles".
    " ON projects.id = projectfiles_projectID";

$res = mysql_query($sql);
if(!$res) die(mysql_error());

if(mysql_num_rows($res) > 0)
{
    $rownum = 0;
    while($row = mysql_fetch_assoc($res))
    {
        print_r($row);
        echo "<br/><br/>";
    $rownum++;
    }
}

Output:

Which is weird because there is only one row in projects but 3 in projectfiles with that projectID… what am I doing wrong?

Answer 1

To select only from the projectfiles table:

$sql = "SELECT projectfiles.*,
        projects.id as projects_id
       FROM projects";

// rest of the code is the same

Update

$sql = "SELECT projectfiles.* FROM projects";
// rest of the code is the same