TSQL：从字符串转换日期和/或时间时转换失败

Question

I had a query that was working but after importing again one table I see the following problem when converting a Varchar into DateTime.

I have the following problem when running the following query:

select FORMAT(convert (datetime,date)  ,   'ddMMyyyy')  from  kat.[dbo].[myTable]

If I try the following I see the same problem:

SELECT convert(datetime, date, 126) from kat.[dbo].[myTable]

The dates that I have in the main table follow the same format:

2017-09-01

EDit with Data Screenshot for the Format:

MAny thanks in advance,

Kat

Answer 1

The dates that I have in the main table follow the same format:

 2017-09-01

There are some stings in your table that have different format.

Try to catch them with this code:

select *
from kat.[dbo].[myTable]
where dt not like '[1-9][0-9][0-9][0-9]-[0-1][0-9]-[0-3][0-9]';

In future, don't store datetime values as strings, use datetime / date .

UPDATE

So it's not true that your strings are like '2017-09-01' Here is my example with your date:

declare @t table (dt varchar(20));
insert into @t values ('2017-09-01');

select *
from @t
where dt not like '[1-9][0-9][0-9][0-9]-[0-1][0-9]-[0-3][0-9]';

My code returns no rows because '2017-09-01' reflects the format you inicated, and if it returns all rows in your case, the format is different.

Answer 2

I actually think strings cannot be converted directly to dates (at least not when you use CAST)... Why not convert the string to an int first?

Assuming your column is named [Date], I would stick with:

SELECT
cast(DATEADD(DAY, cast([Date] as int), -2) as date) as [Date]
FROM kat.[dbo].[myTable]

If you have a different column name, here is the template:

SELECT
cast(DATEADD(DAY, cast([MyColumnName] as int), -2) as date) as [MyColumnName]
FROM kat.[dbo].[myTable]

Alternatively, I've also updated your code using CONVERT (which honestly I rarely every use so it could be wrong)

SELECT convert(datetime, convert(int, [Date]), 126) from kat.[dbo].[myTable]