Using T-SQL DATEFROMPARTS to return NULL instead of throw error

Question

Often I\'ve received dates in the form of some combination of integers or a single 8 digit integer. To convert them to a usable date I tried the DATEFROMPARTS function but when

Answer 1

I am not sure that I understood you right, but it might help:

DECLARE @year VARCHAR(100)= '1993';
DECLARE @month VARCHAR(100)= '12';
DECLARE @day VARCHAR(100)= '01';


SELECT CASE 
WHEN  ISNUMERIC(@year) = 0 OR  ISNUMERIC(@month) = 0 OR  ISNUMERIC(@day) = 0 THEN NULL
WHEN @year BETWEEN 1 AND 9999 AND (@month BETWEEN 1 AND 12 AND @day BETWEEN 1 AND 28
       OR @month IN(1, 3, 5, 7, 8, 10, 12) AND @day BETWEEN 1 AND 31
       OR @month IN(4, 6, 9, 11) AND @day BETWEEN 1 AND 30
       OR @month = 2 AND @day BETWEEN 1 and CASE WHEN NOT @year % 4 = 0 THEN 28 WHEN NOT @year % 100 = 0 THEN 29 WHEN NOT @year % 400 = 0 THEN 28 ELSE 29 END)
     THEN DATEFROMPARTS(@year, @month, @day) END;

OUTPUT:

1993-12-01

DECLARE @year VARCHAR(100)= '1993';
DECLARE @month VARCHAR(100)= 'Jan';
DECLARE @day VARCHAR(100)= '01';


SELECT CASE 
WHEN  ISNUMERIC(@year) = 0 OR  ISNUMERIC(@month) = 0 OR  ISNUMERIC(@day) = 0 THEN NULL
WHEN @year BETWEEN 1 AND 9999 AND (@month BETWEEN 1 AND 12 AND @day BETWEEN 1 AND 28
       OR @month IN(1, 3, 5, 7, 8, 10, 12) AND @day BETWEEN 1 AND 31
       OR @month IN(4, 6, 9, 11) AND @day BETWEEN 1 AND 30
       OR @month = 2 AND @day BETWEEN 1 and CASE WHEN NOT @year % 4 = 0 THEN 28 WHEN NOT @year % 100 = 0 THEN 29 WHEN NOT @year % 400 = 0 THEN 28 ELSE 29 END)
     THEN DATEFROMPARTS(@year, @month, @day) END;

OUTPUT:

NULL