如何在查询中进行子选择？

Question

Like this my query is working fine:

$pdo = $db->prepare('SELECT *
    FROM projects WHERE project_id = :project_id ');  
    $pdo->execute(array('project_id' => $project_id));
    while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {
         echo "ok";
}

But when I add a subselection then I get a blank page:

$pdo = $db->prepare('SELECT *
    (SELECT * FROM animals WHERE projects.animal=animals.id) AS animal
    FROM projects WHERE project_id = :project_id ');  
    $pdo->execute(array('project_id' => $project_id));
    while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {
         echo "ok";
}

What did I do wrong?

Answer 1

You can use INNER JOIN to have both tables.

$pdo = $db->prepare('SELECT *
FROM projects
INNER JOIN animals ON projects.animal=animals.id
WHERE project_id = :project_id ');  
$pdo->execute(array('project_id' => $project_id));
while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {
   echo "ok";
}

Try this query beacuse this query will return all the projects that have an animal associated in table animals.

I think is this that you want

Answer 2

Found this solution:

$pdo = $db->prepare('SELECT *
    FROM projects 
    LEFT JOIN animals ON projects.animal=animals.id
    WHERE project_id = :project_id ');  
    $pdo->execute(array('project_id' => $project_id));
    while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {
         echo "ok";
}