使用 IN 时比较两个 SQL 查询

Question

我有两个 table，例如 Employee 和 Project tables:

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

Project 具有来自 Employee table 的外键。我必须按照 joining_date 的顺序查询 project 和 dept 以及 return Employee。对于以下查询的大数据集，哪个查询会更快？

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() 表达式的外部查询完全没有必要。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

Comparing two SQL queries when using IN

mysql

sql

sql-order-by

where

sql-in