SQL - 限制一行匹配結果

Question

考慮下面的表格，我將如何編寫一個查詢，返回profession.profession當profession.profession_id存在於contractor_has_profession.profession_id，但其限制在一個結果每個profession.profession

所以在這種示例結果將是[編碼器，數據庫，前端]

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，這應該是足夠的：

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

，或者如果我錯了這裏，然後嘗試：

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