以下のときの、SQLの書き方がわからないので教えてください

select B.name from (
select distinct A1.user_id1 user_id from
(select A1.user_id user_id1,A1.skill_id from T_USER_SKILL A1 Where A1.skill_id = 1) A1 inner join
(select A2.user_id user_id4,A2.skill_id from T_USER_SKILL A2 Where A2.skill_id = 2) A4
on A1.user_id1 = A4.user_id4
) A left join T_USER B on A.user_id = B.user_id

こんな感じでいいでしょう。

例を２つほど

該当するスキルを単純に数える方法

SELECT B.name
FROM (
    SELECT user_id
    FROM T_USER_SKILL
    WHERE skill_id in (1, 2)
    GROUP BY user_id
    HAVING count(*) = 2
) A
LEFT JOIN T_USER B ON A.user_id = B.user_id
;

該当するスキルをAND条件で繋ぐ方法

SELECT B.name
FROM (
    SELECT A1.user_id
    FROM T_USER_SKILL A1
    LEFT JOIN  T_USER_SKILL A2 ON A2.user_id = A1.user_id
    WHERE A1.skill_id = 1 AND A2.skill_id = 2
) A
LEFT JOIN T_USER B ON A.user_id = B.user_id
;