Completeness
You need to check both $mysqli and $statement. If they are false, you need to output $mysqli->error or $statement->error respectively.
Efficiency
For simple scripts that may terminate, I use simple one-liners that trigger a PHP error with the message. For a more complex application, an error warning system should be activated instead, for example by throwing an exception.
Usage example 1: Simple script
# This is in a simple command line script
$mysqli = new mysqli('localhost', 'buzUser', 'buzPassword');
$q = "UPDATE foo SET bar=1";
($statement = $mysqli->prepare($q)) or trigger_error($mysqli->error, E_USER_ERROR);
$statement->execute() or trigger_error($statement->error, E_USER_ERROR);
Usage example 2: Application
# This is part of an application
class FuzDatabaseException extends Exception {
}
class Foo {
public $mysqli;
public function __construct(mysqli $mysqli) {
$this->mysqli = $mysqli;
}
public function updateBar() {
$q = "UPDATE foo SET bar=1";
$statement = $this->mysqli->prepare($q);
if (!$statement) {
throw new FuzDatabaseException($mysqli->error);
}
if (!$statement->execute()) {
throw new FuzDatabaseException($statement->error);
}
}
}
$foo = new Foo(new mysqli('localhost','buzUser','buzPassword'));
try {
$foo->updateBar();
} catch (FuzDatabaseException $e)
$msg = $e->getMessage();
// Now send warning emails, write log
}