PDO, MySQL SELECT statement returning boolean true?

Just using a SELECT in my MySQL statement, trying to get a column.

$last_visit = $db->prepare( 'SELECT `last_visit` FROM `开发者_JAVA技巧visitors` WHERE `ip` = :ip' )
        ->execute( $arr_ip );
var_dump( $last_visit );

The output of var_dump is bool(true) instead of the data I need. Trying ->fetch() only throws an error.

What can I do? This is holding up my whole project, and I can't figure out what's wrong no matter where I look. The correct data is in the database, the connection is correct and INSERT works.

as said in the documentation, execute() returns a boolean. take a look at the eamples for fetch() to see how your should use PDO.

In your case, the code should look like this:

$stmt = $db->prepare( 'SELECT `last_visit` FROM `visitors` WHERE `ip` = :ip' );
$stmt->bindParam(':ip', $arr_ip);
$stmt->execute();
if($row = $stmt->fetch()){
  $last_visit = $row['last_visit'];
}else{
  // whatever you like to do if there's no result...
}

EDIT:
additional information in response to your comment:

For an UPDATE or DELETE, you can do a one-liner like your example, because you may not need the result (or rather just true/false to see if the request was successful).

For a SELECT, you need to fetch() the result. You can leave bindParam() out and give the params to execute, like you tried, but without a fetch(), you wont get your results.