Question

我正面临一个问题，我无法理解什么是错的。在我的数据库中，我有一个datetime字段，它保留了一些值：03.10.2012 11:25:06 我需要将其转换为date并将其与其他日期进行比较。我没有成功的尝试是：

p1.value as City,
p2.value as Country,
p3.value as RequestNumber,
convert (datetime, convert (varchar, test.timestampmin, 101), 101) as timestampmin

from Process p
LEFT JOIN Parameter p1 on p1.ID=p.id AND p1.NAME = 'City'
LEFT JOIN Parameter p2 on p2.ID=p.id AND p2.NAME = 'Country'
LEFT JOIN PA_Parameter p3 on p3.ID=p.id AND p3.NAME = 'RequestNumber'

INNER JOIN
(
    SELECT min(Timestamp) as timestampmin, id as id
    FROM tasks
    GROUP BY id
) as test 
    ON test.id = p3.ID

where p.type='Event' and 
timestampmin = convert (datetime, convert (varchar, '06.18.2012', 101), 101)

问题在于我无法将转换后的datetime与我在where子句中使用的convert (datetime, convert (varchar, '06.18.2012', 101), 101)进行比较。我错过了什么？

Answer 1

很简单，您无法在同一查询的WHERE子句中的SELECT子句中访问列别名。

p1.value as City,
p2.value as Country,
p3.value as RequestNumber,
convert (datetime, convert (varchar, test.timestampmin, 101), 101) as timestampmin

from Process p
LEFT JOIN Parameter p1 on p1.ID=p.id AND p1.NAME = 'City'
LEFT JOIN Parameter p2 on p2.ID=p.id AND p2.NAME = 'Country'
LEFT JOIN PA_Parameter p3 on p3.ID=p.id AND p3.NAME = 'RequestNumber'

INNER JOIN
(
    SELECT min(Timestamp) as timestampmin, id as id
    FROM tasks
    GROUP BY id
) as test 
    ON test.id = p3.ID

where p.type='Event' and 
convert (datetime, convert (varchar, test.timestampmin, 101), 101)
   = convert (datetime, convert (varchar, '06.18.2012', 101), 101)

如果test.timestampmin是日期时间列，则可以在WHERE子句中使用它

where p.type='Event'
  and test.timestampmin >= '20120618'
  and test.timestampmin <  '20120619'

无法将日期不时转换并与其他日期进行比较

1 个答案: