SQL将字符串（日期或文本）转换为日期

Question

I have a database which has a column called stringNextDue that contains data like dates (UK format) and text (eg "overdue", "completed")

I am trying to create a view that shows courses that are due within a month from now:

WHERE 
    CONVERT(DATETIME, mt.stringNextDue , 103) < DATEADD(MONTH, 1, GETDATE())

This throws an error:

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

Which is probably due to the fact that stringNextDue may contain actual strings of text.

I tried using

WHERE 
    ISDATE(mt.NextDateString) = 1 
    AND CONVERT(DATETIME, mt.stringNextDue , 103) < DATEADD(MONTH, 1, GETDATE())

But ISDATE only accepts US date formats therefore ignoring a lot of actual dates as strings

Tried set dateformat 'dmy' , which fixed the IsDate issue, but it cannot be used in views.

Any suggestions?

Server update is not an option

Answer 1

If you cannot use the new TRY_CONVERT you might use a function like this:

Attention: This will not catch a wrong date like 31.06.2016, you'd have to modify the BETWEEN 1 AND 31 if you need this...

Attention2: If your text might include characters forbidden in xml you should replace < with < , > with > and & with & ...

CREATE FUNCTION dbo.TestDate(@TestString VARCHAR(100))
RETURNS DATE
AS
BEGIN
    DECLARE @x XML=CAST('<x>' + REPLACE(@TestString,'.','</x><x>') + '</x>' AS XML)

    DECLARE @p1 VARCHAR(10) = @x.value('x[1]','varchar(10)');
    DECLARE @p2 VARCHAR(10) = @x.value('x[2]','varchar(10)');
    DECLARE @p3 VARCHAR(10) = @x.value('x[3]','varchar(10)');

    IF    LEN(@p1)=2 AND ISNUMERIC(@p1)=1 AND CAST(@p1 AS INT) BETWEEN 1 AND 31
      AND LEN(@p2)=2 AND ISNUMERIC(@p2)=1 AND CAST(@p2 AS INT) BETWEEN 1 AND 12
      AND LEN(@p3)=4 AND ISNUMERIC(@p3)=1 AND CAST(@p3 AS INT) BETWEEN 1900 AND 2100

    RETURN CONVERT(DATETIME, @TestString , 103);

    RETURN NULL;
END
GO

SELECT
  dbo.TestDate('overdue') AS SureNoDate
 ,dbo.TestDate('01.04.2016') AS EuropeanDate
 ,dbo.TestDate('2016.04.01') AS WrongFormat
 ,dbo.TestDate('01.13.2016') AS BadDate;
GO

DROP FUNCTION dbo.TestDate;

The result

SureNoDate  EuropeanDate    WrongFormat BadDate
NULL        2016-04-01      NULL        NULL

You might pass back a valid date ( RETURN GETDATE() ?) instead of RETURN NULL for your comparisson outside. This depends on your needs...

Answer 2

It should be possible to replace WHERE clause using this:

SELECT *
FROM 
  -- sample data
  (values('2015-01-01'),('01-01-2015'), ('x-x-x-x')) mt(NextDateString)
-- Replace WHERE statement with the following
CROSS APPLY
(
  SELECT
    RIGHT('0000'+PARSENAME(REPLACE(mt.NextDateString, '-', '.'), 1),4) yyy,
    RIGHT('0000'+PARSENAME(REPLACE(mt.NextDateString, '-', '.'), 2),4) mmm,
    RIGHT('0000'+PARSENAME(REPLACE(mt.NextDateString, '-', '.'), 3),4) ddd
) x
WHERE 
  x.yyy BETWEEN '1950' AND '2050'
  AND x.mmm BETWEEN '0001' AND '0012'
  AND x.ddd BETWEEN '0001' AND '0031'
  AND  ISDATE(mt.NextDateString) = 1
  AND x.yyy+x.mmm+x.ddd < CONVERT(char(8), DATEADD(MONTH, 1, GETDATE()), 112)

Result:

NextDateString  yyy   mmm   ddd
01-01-2015      2015  0001  0001

Answer 3

Thank you for suggestions,

I fixed it by setting language to British on user settings

EXEC sp_defaultlanguage 'username', 'british'