从几个表VS内连接(From several table VS inner join)

从几个表VS内连接(From several table VS inner join)

我不明白这一点。

有什么区别

select e.empid from employee_table e inner join customer_table c on deref(c.infos).personid = deref(e.infos).personid order by e.empid;

和

select e.empid from employee_table e, customer_table c where deref(c.infos).personid = deref(e.infos).personid order by e.empid;

结果是一样的。 一个比另一个更快？

什么时候使用内连接我们可以简单地从多个表中选择？

I can't get the point.

What is the difference between

select e.empid from employee_table e inner join customer_table c on deref(c.infos).personid = deref(e.infos).personid order by e.empid;

and

select e.empid from employee_table e, customer_table c where deref(c.infos).personid = deref(e.infos).personid order by e.empid;

The results are the same. Is one faster to perform than the other ?

When to use an inner join when we can simply select from multiple table ?

最满意答案

因为这两个查询是等价的。 但第一个是使用ANSI-92样式连接，第二个是使用ANSI-89样式连接。 较新的连接语法不容易出错，现在已经存在了25年。

您应该始终使用ANSI-92样式连接。 http://sqlblog.com/blogs/aaron_bertrand/archive/2009/10/08/bad-habits-to-kick-using-old-style-joins.aspx

Because these two queries are equivalent. But the first one is using ANSI-92 style joins and the second is using ANSI-89 style joins. The newer join syntax is less prone to error and it has been around for 25 years now.

You should always use the ANSI-92 style joins.

Bad habits to kick : using old-style JOINs