在同一张桌子上的两个联接

Question

I'm working on a website which shows the soccer score with two teams and two scores in my DB.

This is the code I have:

<?php 
        $result = mysql_query( "SELECT * FROM resultat 
        LEFT JOIN brukere ON resultat.dommer = brukere.id
        INNER JOIN lag ON resultat.lag1 = lag.id
            INNER JOIN lag ON resultat.lag2 = lag.id
        ORDER BY slutt DESC
        " )
        or die("SELECT Error: ".mysql_error());
        $num_rows = mysql_num_rows($result);if ($result) {while ($row = mysql_fetch_array($result)) {
        $_SESSION['id']=$row['id'];
        ?>
        <tr>
                <td><?php echo $row['klubb']; ?></td>
                <td><?php echo $row['klubb']; ?></td>
                <td><?php echo $row['stilling1'] . " - " . $row['stilling2']; ?></td>
                <td><?php echo $row['roed'] . " rødt og " . $row['gult'] . " gult"; ?></td>
                <td><?php echo $row['bane']; ?></td>
                <td><?php echo $row['navn']; ?></td>
            </tr>
        <?php
        }
        }
        ?>

And I get:

SELECT Error: Not unique table/alias: 'lag'

When I try:

INNER JOIN lag s ON resultat.lag1 = lag.id
INNER JOIN lag c ON resultat.lag2 = lag.id

I get:

SELECT Error: Unknown column 'lag.id' in 'on clause'

How do I do it? Two joins from the same table

Answer 1

You need to use the alias you just gave to your table lag . You assigned s at first join and c at second so you should use them

INNER JOIN lag s ON resultat.lag1 = s.id
INNER JOIN lag c ON resultat.lag2 = c.id

Answer 2

You can try to combine JOIN like this:

INNER JOIN lag ON resultat.lag1 = lag.id OR resultat.lag2 = lag.id

Replace OR with AND if you need

Answer 3

This is a self-join and you need the alias in your expession:

     INNER JOIN lag s ON resultat.lag1 = s.id
     INNER JOIN lag c ON resultat.lag2 = c.id 

In general you use self-joins with adjacency-list and to walk the tree down a dimension:

    SELECT t1.name AS lev1, t2.name as lev2, t3.name as lev3, t4.name as lev4
    FROM category AS t1
    LEFT JOIN category AS t2 ON t2.parent = t1.category_id
    LEFT JOIN category AS t3 ON t3.parent = t2.category_id
    LEFT JOIN category AS t4 ON t4.parent = t3.category_id
    WHERE t1.parent is NULL