选择 AS 在 interbase 中不工作答案

【问题标题】：Select AS not working in interbase选择 AS 在 interbase 中不工作
【发布时间】：2011-02-18 13:52:46
【问题描述】：

作品

select payeeid, EXTRACT(WEEKDAY FROM checkdate) as DOW, 
(bankcleared - checkdate) as DateDiff  
from Master  
where (bankcleared is not null)  
order by payeeid, DOW, DateDiff

将DateDiff 添加到Where - 不起作用

select payeeid, EXTRACT(WEEKDAY FROM checkdate) as DOW, 
(bankcleared - checkdate) as DateDiff  
from Master  
where (bankcleared is not null)  AND (DateDiff >= 1)  
order by payeeid, DOW, DateDiff

【问题讨论】：

对不起，我也想问....为什么将 DateDiff 添加到 where 会导致错误 - DateDiff Column unknown
因为 DATEDIFF 是一个内置函数，它检索两个日期时间戳之间的日期部分差异。

标签： sql delphi interbase

【解决方案1】：

您只能在 GROUP BY、ORDER BY 或 HAVING 子句中使用列别名。

标准 SQL 不允许您在 WHERE 子句中引用列别名。施加此限制是因为在执行 WHERE 代码时，可能尚未确定列值。

试试这个

select payeeid, EXTRACT(WEEKDAY FROM checkdate) as DOW, 
(bankcleared - checkdate) as DateDiff
from Master
where (bankcleared is not null) AND ((bankcleared - checkdate)>= 1)
order by payeeid, DOW, DateDiff

Unknown Column In Where Clause

【讨论】：

【解决方案2】：

select payeeid, 
       EXTRACT(WEEKDAY FROM checkdate) as DOW, 
       (bankcleared - checkdate) as DateDiff
from Master
WHERE (bankcleared is not null) 
AND   ((bankcleared - checkdate)>= 1)
Order by  payeeid, DOW, DateDiff

【讨论】：