QUAIS OS PROBLEMAS DESSE CODIGO COMO POSSO RESOLVER?

$usuario=$ _POST["usuario"];
$senha=$ _POST["senha"];
$connection = pg_pconnect('host=localhost port=5432 dbname=corridas user=postgres password=postgres');
if($connection){
$query="SELECT name FROM usuarios WHERE username='.$usuario.' AND password='.$senha.';";
$result= pg_query($connection,$query) or die("Erro na query: [$query]".pg_last_error($connection));
if(pg_num_rows($result)==1){
$dados=pg_fetch_row($result);
header("location:principal.php");
}else{
header("location:index.php");
}
}
else {
echo "
problemas ao acessar o BD
n";
echo "voltarn";
}
?>