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，然后按Employee的顺序返回joining_date。哪个查询在下面的查询中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

或者有更好更简单的方法吗？

Answer 1

使用IN()表达式的外部查询没有用处是完全没必要的。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

使用IN时比较两个SQL查询

1 个答案: