DateAdd / conversion

Question

使用这个简单的查询

SELECT dateadd(d,-13,Period_DateEnd) Period
FROM ReportingPeriod_tbl

一旦我添加了更大的查询，我就会收到转换错误，而且我无能为力。

  

＆＃39;从字符串转换日期和/或时间时转换失败。＆＃39;

SELECT PeriodEnding FROM 
(
SELECT format(WeekEnd,'d-MMM-yy') PeriodEnding
FROM WeekEnd_tbl WHERE WeekEnd <= (SELECT TOP 1 WeekEnd FROM WeekEnd_tbl A WHERE A.IsCurrentWeek = 1)
UNION ALL
SELECT 
    format(Period_DateEnd,'MMM-yy') Period
FROM ReportingPeriod_tbl WHERE ReportingPeriod_ID <= (SELECT TOP 1 ReportingPeriod_ID FROM ReportingPeriod_tbl A 
WHERE Period_DateEnd >= (SELECT TOP 1 WeekEnd FROM WeekEnd_tbl A WHERE A.IsCurrentWeek = 1 ORDER BY WeekEnd))
UNION ALL
SELECT 
    dateadd(d,-13,Period_DateEnd) Period
FROM ReportingPeriod_tbl WHERE ReportingPeriod_ID <= (SELECT TOP 1 ReportingPeriod_ID FROM ReportingPeriod_tbl A 
WHERE Period_DateEnd >= (SELECT TOP 1 WeekEnd FROM WeekEnd_tbl A WHERE A.IsCurrentWeek = 1 ORDER BY WeekEnd))
) Period 

Answer 1

你的字符串日期时间格式是worng

示例：

select  dateadd(d,-13,'2018/04/28 12:00:00.000') --fine be ok
select  dateadd(d,-13,convert(datetime,'2018/04/28 12:00:00.000')) --fine be ok
select  dateadd(d,-13,'04/28')  --Conversion failed when converting date and/or time from character string

希望能帮到你:)。

新Qeustion：

更改您的查询：

SELECT 
    dateadd(d,-13,Period_DateEnd) Period
FROM ReportingPeriod_tbl

到

SELECT 
    dateadd(d,-13,
        SUBSTRING(Period_DateEnd, 7, 4)  
        +'/'+SUBSTRING(Period_DateEnd, 4, 2) 
        +'/'+SUBSTRING(Period_DateEnd, 1, 2) 
        +SUBSTRING(Period_DateEnd, 11, 13)           
    ) Period
FROM ReportingPeriod_tbl

DEMO 和 结果：

Answer 2

请使用它来避免异常并找出格式不正确的strigs：

SELECT 
     [Period]       =   dateadd(d, -13, try_convert(datetime, [Period_DateEnd]))
    ,[Err_message]  =   iif(try_convert(datetime, [Period_DateEnd]) is null, 'Failed to convert string {' + [Period_DateEnd] + '} to datetime', null)
FROM
    [ReportingPeriod_tbl];

完整查询：https://pastebin.com/3PPpkf2t

还有一件事：你必须拥有相同的日期时间格式。为什么？因为03/01/08。是2008年3月1日，或2008年1月3日，或2003年1月8日？ ：）