PDO 从数据库中获取数据

Question

I started using PDO recently, earlier I was using just MySQL. Now I am trying to get all data from database.

$getUsers = $DBH->prepare("SELECT * FROM users ORDER BY id ASC");
$getUsers->fetchAll();
if(count($getUsers) > 0){
    while($user = $getUsers->fetch()){
        echo $user['username']."<br/>";
    }
}else{
    error('No users.');
}

But it is not showing any users, just a blank page.

Answer 1

The PDO method fetchAll() returns an array/result-set, which you need to assign to a variable and then use/iterate through that variable:

$users = $getUsers->fetchAll();
foreach ($users as $user) {
    echo $user['username'] . '<br />';
}

UPDATE (missing execute() )
Also, it appears you aren't calling the execute() method which needs to happen after you prepare the statement but before you actually fetch the data:

$getUsers = $DBH->prepare("SELECT * FROM users ORDER BY id ASC");
$getUsers->execute();
$users = $getUsers->fetchAll();
...

Answer 2

This code below will do what you are asking for:

$sql = $dbh->prepare("SELECT * FROM users ORDER BY id ASC");
$sql->execute();
while ($result = $sql->fetch(PDO::FETCH_ASSOC)) {
    echo $result['username']."<br/>";
}

Answer 3

Your code is missing a call to execute() after prepare() . After your prepared statement is executed you can get the array of records using fetchAll() .

$getUsers = $DBH->prepare('SELECT * FROM users ORDER BY id ASC');
$getUsers->execute();
$users = $getUsers->fetchAll();

// Then in your presentation logic you can use the following code to display the data:
if ($users) {
    foreach ($users as $user) {
        echo $user['username']."<br/>";
    }
} else {
    // Whatever your requirement is to handle the no user case, do it here.
    echo 'Error: No users.';
}

However, in you example you are not passing any variable data to the query and you only execute it once, which defeats a purpose of having prepared statement. You should use prepared statements if you need to have variables in your SQL, for example:

$getUsers = $DBH->prepare('SELECT * FROM users WHERE id=?');
$getUsers->execute([
    $_GET['user_id']
]);
$user = $getUsers->fetch();     // get single user by unique id

If there are no variables then you can simply use query() method.

$users = $DBH->query('SELECT * FROM users ORDER BY id ASC')->fetchAll();

If you do not need to fetch all records at once, you can simply loop on the statement with foreach :

$getUsers = $DBH->prepare('SELECT * FROM users WHERE username LIKE ? ORDER BY id ASC');
$getUsers->execute([
    '%' . $_GET['search'] . '%'     // search for username with wildcards
]);

foreach ($getUsers as $user) {
    echo $user['username']."<br/>";
}