Convert DateTime with NULL value - sql

Question

I am running this query
select * from dbo.CHARGES m
LEFT JOIN Docs z ON z.DocId=m.DocId
AND CHARGE_DATE=CAST(z.DocDate + z.DocTime AS DATETIME)
And getting Conversion failed when converting date and/or time from character string, since some rows of DocDate, DocTime have null value
Here DocTime is Varchar(5)
How can i run this query by ignoring NULL or wrong values?

Answer 1

If your strings are in the format yyyy-MM-dd hh:mm then your convert expression will be something like:
SELECT CONVERT(DATETIME, ISNULL(DocDate, '1900-01-01') + ' ' + ISNULL(DocTime, '00:00'), 121)
However, it is probably adivisable to check that it actually is a date before you try to convert it:
SET DATEFORMAT YMD;
SELECT DocDate,
DocTime,
Formatted = CASE WHEN ISDATE(ISNULL(DocDate, '1900-01-01')
+ ' ' + ISNULL(DocTime, '00:00')) = 1
THEN CONVERT(DATETIME, ISNULL(DocDate, '1900-01-01')
+ ' ' + ISNULL(DocTime, '00:00'), 121)
ELSE NULL
END
FROM (VALUES
('2013-10-01', '17:30'),-- CORRECT FORMAT
('2013-10-01', NULL), -- NULL TIME
('2013-13-10', '17:30'), -- INVALID DATE
('2013-01-05', 'XX:30'), -- INVALID TIME
(NULL, '17:00') -- NULL DATE
) t (DocDate, DocTime);
Note, I have set the dateformat even though it is set within the convert, this is for the benefit of ISDATE(), if the date format is not set this way, it may think that 2013-13-10 is a valid date (13th October 2013), but will through an error when it comes to the convert.
If/When you upgrade to SQL-Server 2012 you can simply use TRY_CONVERT:
SET DATEFORMAT YMD;
SELECT DocDate,
DocTime,
Formatted = TRY_CONVERT(DATETIME, ISNULL(DocDate, '1900-01-01')
+ ' ' + ISNULL(DocTime, '00:00'), 121)
FROM (VALUES
('2013-10-01', '17:30'),-- CORRECT FORMAT
('2013-10-01', NULL), -- NULL TIME
('2013-13-10', '17:30'), -- INVALID DATE
('2013-01-05', 'XX:30'), -- INVALID TIME
(NULL, '17:00') -- NULL DATE
) t (DocDate, DocTime);
Examples on SQL Fiddle
I don't condone this approach, and (as I have in a comment) would strongly advise correcting the problem (which is storing data as the wrong type) rather than jumping through hoops to work around data errors.

Answer 2

Try this code, the query depend of your necessity.
With Null Values
select * from dbo.CHARGES m
LEFT JOIN Docs z
ON z.DocId=m.DocId
AND (
z.DocDate IS NULL
OR z.DocTime IS NULL
OR CHARGE_DATE=CAST(z.DocDate + z.DocTime AS DATETIME)
)
Without Null Values
select * from dbo.CHARGES m
LEFT JOIN Docs z
ON z.DocId=m.DocId
AND (
NOT z.DocDate IS NULL
AND NOT z.DocTime IS NULL
AND CHARGE_DATE=CAST(z.DocDate + z.DocTime AS DATETIME)
)