with users(id, username) as (
    select 1, 'иван' from dual union all
    select 2, 'виктор' from dual
),
clothes(id, userid, clothes, type) as (
    select 1, 1, 'рубашка', 'белая' from dual union all
    select 2, 1, 'брюки', 'чёрные' from dual union all
    select 3, 2, 'рубашка', 'синяя' from dual
)
select * from (
    select username "пользователь", clothes, type from users u, clothes c where u.id = c.userid
)
pivot (
    max(type) for clothes in ('рубашка' "рубашка", 'брюки' "брюки")
)

with users(id, username) as (
    select 1, 'иван' from dual union all
    select 2, 'виктор' from dual
),
clothes(id, userid, clothes, type) as (
    select 1, 1, 'рубашка', 'белая' from dual union all
    select 2, 1, 'брюки', 'чёрные' from dual union all
    select 3, 2, 'рубашка', 'синяя' from dual
)
select 
    username "пользователь", 
    max(case clothes when 'рубашка' then type end) "рубашка",
    max(case clothes when 'брюки' then type end) "брюки"
from users u, clothes c where u.id = c.userid
group by username