Include custom post type single template, but respect theme override of template if it exists

You can use locate_template() first. If this returns anything but an empty string '' then the template exists either in parent or child theme.

if( '' === locate_template( 'custom-single.php' ) ) {
    // Replace given template with your template path.
}

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)