在mysql中使用别名无法正常工作

Question

I am confused by the usage of alias . For example, the query below works fine

select * from 
(
select ROW_NUMBER() over (partition by prodid order by quantity desc) as 'rankin',prodid,quantity from sales
) A
where rankin=1

But when I modify it as shown in the snippet below I get the error: "Invalid column name 'rownumber'".

select ROW_NUMBER() over (order by quantity) as 'rownumber' from sales
where rownumber = 1

Please explain the difference.

Answer 1

这是因为SELECT在WHERE之后执行，而FROM在WHERE之前执行，因此它不能在第二个查询中使用，但可以在第一个查询中使用。