原因别名适用于 ORDER BY 但不适用于 WHERE

Question

我理解 I can't reference an alias in the WHERE clause，但这是为什么呢？是否有不同的解释？

这样的事情会产生错误：

declare @myTable table 
(
    num numeric(5,2),
    den numeric(5,2)
)
insert into @mytable 
select 1, 2
union
select 1, 3
union
select 2, 3
union
select 2, 4
union
select 2, 5
union
select null, 1

select num/den as 'calc' from @myTable
where calc is not null
order by calc

但是这 returns 行：

declare @myTable table 
(
    num numeric(5,2),
    den numeric(5,2)
)
insert into @mytable 
select 1, 2
union
select 1, 3
union
select 2, 3
union
select 2, 4
union
select 2, 5
union
select null, 1

select num/den as 'calc' from @myTable
--where calc is not null
order by calc

Answer 1

如中所述，这是由于自然查询处理顺序：

1. FROM
2. ON
3. OUTER
4. WHERE
5. GROUP BY
6. CUBE | ROLLUP
7. HAVING
8. SELECT
9. DISTINCT
10. ORDER BY
11. TOP