过滤别名列

Question

我在 MS-Access 中有以下查询，运行正常：

SELECT A1.LRN, A1.StartDate, A1.Destination, 
(
    SELECT TOP 1 A2.StartDate
    FROM testEnrolment As A2
    WHERE A2.LRN = A1.LRN AND A2.StartDate > A1.StartDate
    ORDER BY A2.StartDate
) As NextStartDate, 
(
    SELECT TOP 1 B2.Destination
    FROM testEnrolment As B2
    WHERE B2.LRN = A1.LRN AND B2.StartDate > A1.StartDate
    ORDER BY B2.StartDate
) As NextDestination
FROM testEnrolment As A1

2 个别名列 NextStartDate、NextDestination 从当前 LRN 的下一条记录的 StartDate 和 Destination 字段获取数据。

所以如果 table testEnrolment 有这个数据：

LRN    StartDate    Destination
--------------------------------
L0001  01/08/2014   Unemployed
L0001  02/08/2014   Education
L0001  03/08/2014   Unemployed
L0002  20/09/2014   Education
L0002  21/09/2014

查询结果如下：

LRN    StartDate   Destination  NextStartDate  NextDestination
--------------------------------------------------------------
L0001  01/08/2014  Unemployed   02/08/2014     Education
L0001  02/08/2014  Education    03/08/2014     Unemployed
L0001  03/08/2014  Unemployed
L0002  20/09/2014  Education    21/09/2014
L0002  21/09/2014

我接下来要做的是通过 不等于 "Education".

的记录过滤列别名 NextDestination

WHERE 子句对列别名不起作用，我似乎也无法使 HAVING 起作用。

Answer 1

将您的 sql 包装到子查询中，以便您可以过滤别名

SELECT * FROM (
SELECT A1.LRN, A1.StartDate, A1.Destination, 
(
    SELECT TOP 1 A2.StartDate
    FROM testEnrolment As A2
    WHERE A2.LRN = A1.LRN AND A2.StartDate > A1.StartDate
    ORDER BY A2.StartDate
) As NextStartDate, 
(
    SELECT TOP 1 B2.Destination
    FROM testEnrolment As B2
    WHERE B2.LRN = A1.LRN AND B2.StartDate > A1.StartDate
    ORDER BY B2.StartDate
) As NextDestination
FROM testEnrolment As A1
) AS s
WHERE NextDestination <> 'Education'

过滤别名列

Filtering an aliased column

sql

ms-access

jet