如何将这个有效的mysql语句有效地转换为PDO？

Question

I'm trying to convert to using PDO, but can't seem to get results from my PDO while loop.

This mysql statement gives me results:

$q = mysql_query("SELECT * FROM artist ORDER BY artist ASC");
while ($row = mysql_fetch_array($q)) {
  $theartist .= '<option value="'.($row['artist_id']).'">'.($row['artist'])."</option>";
}    

PDO database connection (that appears to work)

//the below isn't throwing any errors
$host='localhost';
$dbname='james_test';
$user='test';
$pass='testpass';

try {
  # MySQL with PDO_MYSQL
  $DBH = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
}
catch(PDOException $e) {
    echo $e->getMessage();
}

This PDO statement does not give me any results:

$query = $DBH->prepare("SELECT * FROM artist ORDER BY artist ASC");
while($row = $query->fetch(PDO::FETCH_ASSOC)) {
    $theartist .= '<option value="'.($row['artist_id']).'">'.($row['artist'])."</option>";
}

Answer 1

You missed the step where you run the query. With a PDO, you can prepare the query which optimises performance and helps prevent SQL injection, but you must still "execute" the statement.

$query = $DBH->prepare("SELECT * FROM artist ORDER BY artist ASC");
$result = $query->execute();
while($row = $result->fetch(PDO::FETCH_ASSOC)) {
    $theartist .= '<option value="'.($row['artist_id']).'">'.($row['artist'])."</option>";
}

Related PHP manual entries:

http://php.net/manual/en/pdostatement.execute.php

http://php.net/manual/en/pdo.prepare.php

Answer 2

This just makes it work by slightly changing your code.

//$query = $DBH->prepare("SELECT * FROM artist ORDER BY artist ASC");
$rows = $DBH->query("SELECT * FROM artist ORDER BY artist ASC");

//while($row = $query->fetch(PDO::FETCH_ASSOC)) {
if ($rows) {
  foreach ($rows as $row) {
      $theartist .= ''.($row['artist'])."";
  }
}

Edit: The query function does both prepare and execute in one go and is useful if you don't have variables to use in the query.