SQL varchar 列到具有 2 个标准的日期列

Question

I have a table with a column varchar(2048) and inside I have data in date format.

But my data is in the format "20/12/2021" (British standard) and also "12/20/2021" (US standard).

Can I convert the varchar column in a date column with both standards?

Answer 1

This is a data/business problem and so will need further decisions by someone who knows the data/business.

As you do not know what format this data is in, you can work out some, but not all - for example:

SELECT 
    *,
    SUBSTRING(D.Date, 0, CHARINDEX('/', D.Date)),
    SUBSTRING(D.Date, CHARINDEX('/', D.Date) + 1, CHARINDEX('/', D.Date, CHARINDEX('/', D.Date)) - 1),

    CASE 
        WHEN SUBSTRING(D.Date, 0, CHARINDEX('/', D.Date)) > 12 THEN 'UK Date'
        WHEN SUBSTRING(D.Date, CHARINDEX('/', D.Date) + 1, CHARINDEX('/', D.Date, CHARINDEX('/', D.Date)) - 1) > 12 THEN 'US Date'
        ELSE 'Indeterminate Date'
    END
FROM 
    ( VALUES 
        ('30/05/2020'),
        ('10/25/2020'),
        ('08/06/2020')
    ) AS D (Date);

You would need to prepare a list of the indeterminate dates and use other information from your data to work out which is which. For example, if these are order dates and there are also shipping dates you could work out because you expect the dates to be close:

Order Date: 02/06/2020 Shipping Date: 02/09/2020

Therefore (unless your company takes 3 months to despatch), this is an American date.