MySQL 嵌入式 SELECT 与 JOIN

Question

两者之间是否存在显着差异:

SELECT userid, username, userdept,
    (SELECT deptname FROM depts WHERE deptid=userdept) AS deptname
    FROM users

和

SELECT userid, username FROM users
    INNER JOIN depts ON depts.deptid=users.userdept

哪个更好？

Answer 1

您的第二个查询具有更好的性能。

你可以看到这个例子:http://www.codersrevolution.com/index.cfm/2008/7/31/MySQL-performance-INNER-JOIN-vs-subselect