How do I select a MySQL database to use with PDO in PHP?

Question

I want to select a MySQL database to use after a PHP PDO object has already been created. How do I do this?

// create PDO object and connect to MySQL
$dbh =         


        

Answer 1

Typically you would specify the database in the DSN when you connect. But if you're creating a new database, obviously you can't specify that database the DSN before you create it.

You can change your default database with the USE statement:

$dbh = new PDO("mysql:host=...;dbname=mysql", ...);

$dbh->query("create database newdatabase");

$dbh->query("use newdatabase");

Subsequent CREATE TABLE statements will be created in your newdatabase.

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Re comment from @Mike:

When you switch databases like that it appears to force PDO to emulate prepared statements. Setting PDO::ATTR_EMULATE_PREPARES to false and then trying to use another database will fail.

I just did some tests and I don't see that happening. Changing the database only happens on the server, and it does not change anything about PDO's configuration in the client. Here's an example:

setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
} catch(PDOException $err) {
    die($err->getMessage());
}

$stmt = $pdo->prepare("select * from foo WHERE i = :i");
$result = $stmt->execute(array("i"=>123));
print_r($stmt->fetchAll(PDO::FETCH_ASSOC));

$pdo->exec("use test2");

$stmt = $pdo->prepare("select * from foo2 WHERE i = :i AND i = :i");
$result = $stmt->execute(array("i"=>456));
print_r($stmt->fetchAll(PDO::FETCH_ASSOC));

If what you're saying is true, then this should work without error. PDO can use a given named parameter more than once only if PDO::ATTR_EMULATE_PREPARES is true. So if you're saying that this attribute is set to true as a side effect of changing databases, then it should work.

But it doesn't work -- it gets an error "Invalid parameter number" which indicates that non-emulated prepared statements remains in effect.