You should not use raw SQL to modify roles and capabilities, it is very bad practice, and unnecessary.
Instead, use the roles API, e.g.
$role = get_role( 'subscriber' );
$role->add_cap( 'read' );
Or to add it to a specific user:
$user = new WP_User( $user_id );
$user->add_cap( 'read' );
Likewise you can remove a capability from a role:
$role = get_role( 'subscriber' );
$role->remove_cap( 'read' );