mysql - How canI join a table with itself for a query in a PHP script, and tell the script which column to pick from which table?

Solution:

You actually have table aliases (c and cc). So you need aliases for your attributes. I mean something like this:

$sql = "SELECT DISTINCT c.co_name as nameA, cc.co_name as nameB
        FROM Deliveries d 
            INNER JOIN Companies c ON d.id_co = c.id_co, 
                                Deliveries dd 
            INNER JOIN Companies cc ON dd.id_co = cc.id_co

        WHERE d.id_obj = dd.id_obj 
        AND d.id_sup = dd.id_sup 
        AND d.id_co < dd.id_co";
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Later use your echo line like this:

echo "<tr><td>".$row["nameA"]."</td><td>".$row["nameB"]."</td></tr>";
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Hope it helps you...