returnOptional.ofNullable(entityManager.createNativeQuery("select `map` from `"+db+"`.`user_connections` WHERE 1 ORDER BY `user_connections`.`id` DESC LIMIT 1")
//.setParameter(1, db)
publicOptional<List>getMap(Stringdb,intlimit){
returnOptional.ofNullable(entityManager.createNativeQuery("select distinct `map` from `"+db+"`.`user_connections` WHERE 1 ORDER BY `user_connections`.`id` DESC LIMIT ?1")