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WHERE语句中无法识别列别名

column-alias database mysql sql

Ben · 技术社区 · 15 年前

我创建的一个查询有一个奇怪的“问题”。下一个问题是:

 SELECT 
 ID,
 DistanceFromUtrecht,
 (
  SELECT
   (MAX(DateUntil) - (ReleaseDays * 60 * 60 * 24))
  FROM
   PricePeriod
  WHERE
   PricePeriod.FK_Accommodation = Accommodation.ID
 ) AS LatestBookableTimestamp
FROM
 Accommodation
WHERE
 LatestBookableTimestamp < UNIX_TIMESTAMP()

phpMyAdmin一直抛出一个错误,关于没有一个名为'LatestBookableTimestamp'的列,即使我有一个由子查询检索的列,该别名也是如此。我也尝试过用tableprefix选择每一列。这不管用。最后,我用一个表别名选择了所有的列,并给了这个表一个别名。都没有运气。

4 回复 | 直到 14 年前

Mchl 15 年前

使用HAVING

HAVING
  LatestBookableTimestamp < UNIX_TIMESTAMP()

另一方面,您使用的是dependednt子查询,这在性能方面是个坏主意。

试着这样做:

SELECT 
  a.ID,
  a.DistanceFromUtrecht,
  pp.LatestBookableTimestamp
FROM
  Accommodation AS a
INNER JOIN (
  SELECT
    FK_Accommodation,
    MAX(DateUntil) - (ReleaseDays * 60 * 60 * 24) AS LatestBookableTimestamp
  FROM 
    PricePeriod 
  GROUP BY 
    FK_Accommodation
) AS pp    
ON pp.FK_Accommodation = a.ID    
WHERE
  pp.LatestBookableTimestamp < UNIX_TIMESTAMP()

OMG Ponies 15 年前

不能在WHERE子句中使用列别名。
MySQL(和sqlserver)将允许在groupby中使用列别名,但并不广泛支持。ORDER BY是支持列别名引用的最受一致支持的位置。

   SELECT a.id,
          a.distancefromutrecht,
          b.LatestBookableTimestamp
     FROM ACCOMMODATION a
LEFT JOIN (SELECT pp.fk_accommodation,
                  MAX(DateUntil) - (ReleaseDays * 60 * 60 * 24) AS LatestBookableTimestamp
             FROM PRICEPERIOD pp
         GROUP BY pp.fk_accommodation) b ON b.fk_accommodation = a.id
    WHERE b.LatestBookableTimestamp < UNIX_TIMESTAMP()

Fosco 15 年前

您需要接受原始查询,而不使用where子句,并将其转换为子查询。

select * from (
 SELECT ID, DistanceFromUtrecht, 
 ( 
  SELECT 
   (MAX(DateUntil) - (ReleaseDays * 60 * 60 * 24)) 
  FROM 
   PricePeriod 
  WHERE 
   PricePeriod.FK_Accommodation = Accommodation.ID 
 ) AS LatestBookableTimestamp 
FROM 
 Accommodation 
) a
WHERE 
 LatestBookableTimestamp < UNIX_TIMESTAMP()

D'Arcy Rittich 15 年前

select a.ID, 
    a.DistanceFromUtrecht, MaxDateUntil - (ReleaseDays * 60 * 60 * 24) AS LatestBookableTimestamp 
from (
    SELECT FK_Accommodation, MAX(DateUntil) as MaxDateUntil
    FROM PricePeriod 
    group by FK_Accommodation
) ppm
inner join Accommodation a on ppm.FK_Accommodation = a.ID 
where MaxDateUntil - (ReleaseDays * 60 * 60 * 24) < UNIX_TIMESTAMP()