sql-server-2012 - 为什么这个查询的 CONVERT to datetime 中断而不是另一个？

Question

此查询工作正常：

select CONVERT(DATETIME, GroupAdminEffectiveDate, 101) from ExchangeSmallGroupEnrollment
group by GroupAdminEffectiveDate

并返回以下内容：

1900-01-01 00:00:00.000
2012-06-30 00:00:00.000
2012-07-01 00:00:00.000
2012-07-11 00:00:00.000
2012-07-23 00:00:00.000
2012-07-25 00:00:00.000
2012-08-01 00:00:00.000
2012-08-14 00:00:00.000
2012-08-26 00:00:00.000
2012-09-01 00:00:00.000
2012-09-03 00:00:00.000

但是，以下查询：

select CONVERT(DATETIME, GroupAdminEffectiveDate, 101) from ExchangeSmallGroupEnrollment

我得到以下错误：

Msg 241, Level 16, State 1, Line 1
Conversion failed when converting date and/or time from character string.

有任何想法吗？非常感激。

更新：

询问：

select distinct GroupAdminEffectiveDate from ExchangeSmallGroupEnrollment

结果：

(empty string)
06/30/2012
07/01/2012
07/11/2012
07/23/2012
07/25/2012
08/01/2012
08/14/2012
08/26/2012
09/01/2012
09/03/2012

Answer 1

我无法重现你的错误，所以我怀疑我们对“空字符串”的定义不同，或者还有其他事情你没有透露。同时，由于您使用的是 SQL Server 2012，因此您可以使用TRY_PARSE它，例如以下表达式之一：

SELECT TRY_PARSE(GroupAdminEffectiveDate AS DATETIME USING N'en-us') 
  FROM dbo.ExchangeSmallGroupEnrollment;

SELECT TRY_PARSE(GroupAdminEffectiveDate AS DATETIME USING N'en-us') 
  FROM dbo.ExchangeSmallGroupEnrollment
  GROUP BY GroupAdminEffectiveDate;

SELECT TRY_PARSE(GroupAdminEffectiveDate AS DATETIME USING N'en-us') 
  FROM dbo.ExchangeSmallGroupEnrollment
  GROUP BY TRY_PARSE(GroupAdminEffectiveDate AS DATETIME USING N'en-us');

如果您真的希望 1900-01-01 成为有效输出，则：

SELECT COALESCE(TRY_PARSE(GroupAdminEffectiveDate AS DATETIME USING N'en-us'),
    '19000101') 
  FROM dbo.ExchangeSmallGroupEnrollment
  GROUP BY TRY_PARSE(GroupAdminEffectiveDate AS DATETIME USING N'en-us');

Answer 2

您首先将您的varchar列转换为Datetime然后转换。

Declare @testvarchar VARCHAR(15) = '08/27/2012'
select CONVERT(datetime, Cast(@testvarchar as datetime), 101)

那应该可以解决您的转换错误

Answer 3

您的数据库中可能存在更多“非日期”字段。一个可以""，另一个" "。当您按或区分时，所有最终都""意味着NULL，这很好转换。否则它会失败" "（空间）。

检查select length( GroupAdminEffectiveDate ) from ExchangeSmallGroupEnrollment 也许它会给你一些线索？

Answer 4

检查这个：

select CONVERT(DATETIME, ISDATE( GroupAdminEffectiveDate), 101) from ExchangeSmallGroupEnrollment