DROP TABLE if EXISTS aux;
create table aux(line int);
insert into aux(line) values(1);
insert into aux(line) values(2);

SELECT label FROM (SELECT DISTINCT ELT(aux.line,pnm.first,pnm.second) all_n FROM politmap_neighbor as pnm
left JOIN politmap pm ON pm.label='South_Arabian_Sea'
CROSS JOIN aux
WHERE pnm.first=pm.id OR pnm.second=pm.id) AS pppp
LEFT JOIN politmap fpm ON fpm.id=all_n;
DROP TABLE if EXISTS aux;

select name from (
select User2ID AS uid from Friendship
join Users u1
where User1ID = u1.id and u1.name='Иван'
union
select User1ID AS uid from Friendship
join Users u2 
where User2ID = u2.id
and u2.name='Иван'
) as names 
join Users u3
where u3.id=names.id

sql
select User2ID AS uid from Friendship
join Users u1
on User1ID = u1.id
union
select User1ID AS uid from Friendship
join Users u2 
on User2ID = u2.id