Question

I have an SQL query which displays 2 rows retrieved but when I echo the field name nothing is retrieved. Anyone know what I am doing wrong?

$sql = 'SELECT *
FROM tag_map
LEFT JOIN tags2 ON tags2.tag_id = tag_map.tag_id
LEFT JOIN video ON video.vid_id = tag_map.vid_id
WHERE tag_map.vid_id=?';
$stmt_tags = $conn->prepare($sql);
$result=$stmt_tags->execute(array($vid_id));
echo $tag_count=$stmt_tags->rowCount(); //shows 2
$tags = array();
while ($row = $stmt_tags->fetch(PDO::FETCH_ASSOC)) {
    echo $row['name'];
}

EDIT: Var_dump using suggested query

SELECT tag_map.*, tags2.name AS tag_name
FROM tag_map
LEFT JOIN tags2 ON tags2.tag_id = tag_map.tag_id
LEFT JOIN video ON video.vid_id = tag_map.vid_id
WHERE tag_map.vid_id=?


array(4) { ["id"]=> string(4) "1234" ["vid_id"]=> string(32) "8364a8e463052e215a5dc174c92a2f18" ["tag_id"]=> string(32) "4c71a73d001dd9c09c7d9d95907bf1fe" ["tag_name"]=> NULL } array(4) { ["id"]=> string(3) "123" ["vid_id"]=> string(32) "8364a8e463052e215a5dc174c92a2f18" ["tag_id"]=> string(32) "57bb5dd83dc84e7115387886e328b04b" ["tag_name"]=> NULL }

Answer 1

You should be specific in your SELECT clause, particularly when joining other tables.

For example

SELECT tag_map.vid_id, tag_map.name, tags2.name AS tag_name

Notice how I’ve used an alias for tags2.name to avoid a column name conflict with tag_map.name.

I’m only guessing here but I’d say you have a name column in one of your left-joined tables that’s overriding tag_map.name.

Update

In light of the extra information, I’d have to say it’s solely due to your left-joins. The records where tags2.name is showing NULL simply do not have related fields in tag_map for the vid_id in question.

If you only want to show records where there is a relation between tag_map and tags2, use INNER JOIN

Demo here – http://sqlize.com/UL1M80DT0c