Question

I was trying to make a function to work in db2:

CREATE FUNCTION TO_DATE8(DATE_STRING numeric(8,0))
    RETURNS DATE
    LANGUAGE SQL
    IF DATE_STRING > 0 THEN
         // ERROR ->
         RETURN DATE ( TO_DATE ( SUBSTR ( DATE_STRING , 1 , 8 ) , 'YYYYMMDD' ) )
    ELSE
         RETURN  DATE ( TO_DATE ( '00000000' , 'YYYYMMDD' ) ) 
    END IF
END

ERROR: DATE IS NOT VALID

What to do?

Answer 1

The form of the procedure required seems to be like this (at least on the iSeries version):

CREATE FUNCTION TO_DATE8(DATE_STRING numeric(8,0))          
RETURNS DATE                                            
LANGUAGE SQL
BEGIN
    RETURN(CASE WHEN DATE_STRING > 0 THEN DATE(SUBSTR(DATE_STRING, 1, 4) || '-' || 
                                               SUBSTR(DATE_STRING, 5, 2) || '-' || 
                                               SUBSTR(DATE_STRING, 7, 2))
                ELSE DATE('0001-01-01')
                END);
END

However:

• Your procedure is misnamed (reading from a date-8, not to it).
• Your DATE_STRING is not a string (or even a char), it’s numeric. Please rename it to something that does not include the datatype (dateToConvert works)
• You seem to want to return something that is not a valid date (all 0s). I’m returning *loval here, although it’s possible it should actually be null.
• I didn’t put in enough checks for a valid date – this will blow up really easily.
• If at all possible, the database should be changed to contain actual dates, not a numeric value. Disk is (relative to programmer/architect headaches) cheap.
• You may also find a calendar file helpful, if the 8-digit numeric was one of the included columns.