使用 IN 时比较两个 SQL 查询

Question

我有两个表，例如Employee 和Project 表：

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

Project 具有来自Employee 表的外键。 我必须查询project 和dept 并按照joining_date 的顺序返回Employee。哪个查询将在以下查询的大数据集上运行得更快？

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

或者有没有更好更简单的方法？

Answer 1

使用IN() 表达式的外部查询毫无用处是完全没有必要的。这将产生您需要的输出：

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