SQL -将匹配结果限制为一行

Question

考虑到下表，当profession.profession_id存在于contractor_has_profession.profession_id中时，我该如何编写返回profession.profession的查询，但将其限制为每个profession.profession只能返回一个结果

因此，在此示例中，结果将是Coder、Database、Frontend

contractor_has_profession
contractor_id | profession_id
1             | 5
2             | 5
3             | 5
4             | 2
5             | 1

profession
profession_id | profession
1             | Frontend
2             | Database
3             | Graphics
4             | Sound
5             | Coder

Answer 1

SELECT p.profession
FROM   profession p
WHERE  EXISTS(SELECT *
              FROM   contractor_has_profession c
              WHERE  c.profession_id = p.profession_id)  

Answer 2

嗯，这应该足够了：

select distinct p.profession
from profession p
inner join contractor_has_profession c
where p.profession_id = c.profession_id

或者如果我说错了，那就试试：

select p.profession
from profession p
inner join contractor_has_profession c
where p.profession_id = c.profession_id
group by p.profession