约会时间！ 从字符串转换日期和/或时间时转换失败

Question

I tried converting a column with timestamp from nvarchar to datetime (as I wasn't sure that by exporting Excel to SQL Server the precision within timestamp won't be lost), but the column still won't convert, showing the same error all the time

Conversion failed when converting date and/or time from character string - convert

I tried

alter table X 
    alter column [Timestamp] datetime

and I also tried:

convert(datetime, [Timestamp], 103)
try_convert(datetime, [Timestamp], 103)
cast ([Timestamp] as datetime)

still no progress.

This is the sample data from the column:

2019-02-13-13.01.05.6100000015
2019-02-18-13.10.46.4850000015

Could you please help?

Answer 1

You can try this:

select 
    try_convert(datetime2(7), 
                 STUFF(STUFF(REPLACE('2019-02-18-13.10.46.485000015','.',':'), 11, 1, ' '),20,1,'.')
               ,121)

Answer 2

It's probably best to change the type to a DATETIME2 since it has a higher precision than DATETIME.

First change the format of the timestamp strings to a format that can be casted to a DATETIME2 without problem.

UPDATE X
SET [Timestamp] = CONCAT(LEFT([Timestamp],10), 'T', REPLACE(SUBSTRING([Timestamp],12,8),'.',':'),  '.', SUBSTRING([Timestamp],21,9))
WHERE [Timestamp] LIKE '[12][0-9][0-9][0-9]_[01][0-9]_[0-3][0-9]_[0-2][0-9].[0-6][0-9].[0-6][0-9].[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]%';

Then double check if there are still some that can't be casted as-is.

SELECT COUNT(*) Errors, MAX([Timestamp]) Example
FROM X
WHERE TRY_CAST([Timestamp] AS DATETIME2) IS NULL;

If the count was 0 then the type of the column can be changed.

ALTER TABLE X 
  ALTER COLUMN [Timestamp] DATETIME2(7);

A test on rextester here

Do notice that some precision will be lost.