當使用IN

Question

我有兩個表，例如Employee和Project表比較兩個SQL查詢：

Employee (id, dept, joining_date) 
Project (emp_id, project) 

隨着Project具有Employee表的外鍵。 我必須在project和dept上查詢，並按joining_date的順序返回Employee。對於下面的查詢中的大數據集，哪種查詢的工作速度會更快？

select * from Employee where id in (select p.emp_id from Project p join Employee e on p.emp_id = e.id where p.project = 'project1' and e.dept = 'dept1') order by joining_date 

select * from Employee where id in (select p.emp_id from Project p join Employee e on p.emp_id = e.id where p.project = 'project1' and e.dept = 'dept1') and dept = 'dept1' order by joining_date 

或者有沒有更好更簡單的方法呢？

Answer 1

使用IN()表達式的外部查詢完全沒有必要。這將產生你需要的輸出：

select e.* 
from Project p 
inner join Employee e on p.emp_id = e.id 
where p.project = 'project1' and e.dept = 'dept1' 
order by joining_date