Better date conversion with timestamp_format

Handling dates and times on the IBM i can often be a bit of a challenge. Obviously, if you are working with a modern application that uses the Date, Time and Timestamp data types everything is nice and straightforward. However, there are plenty of old applications that use eight, seven or six digit numeric fields to represent dates and, sooner or later, you will need to extract these in a manner that looks sane in some other environment.

Timestamp_format is your friend.

The TIMESTAMP_FORMAT function returns a timestamp that is based on the interpretation of the input string using the specified format.

It’s that “interpretation of the input string” that makes this so handy. Put simply: you tell the function how to interpret the string and it will do the rest.

Here’s an example. I have a contracts table (CONTRACTS) with three columns: Contract Number (CTNR), Start Date (STDT) and End Date (ENDT). And the start and end date are both seven digit numbers. I need to list all of the currently active contracts (Start Date is before Today and End Date is after Today).

And the SQL looks like this:

select CTNR,
       date(timestamp_format(substr(digits(STDT), 2, 6), 'YYMMDD')),
       date(timestamp_format(substr(digits(ENDT), 2, 6), 'YYMMDD'))
from CONTRACTS
where date(timestamp_format(substr(digits(STDT), 2, 6), 'YYMMDD')) <= current_date
and date(timestamp_format(substr(digits(ENDT), 2, 6), 'YYMMDD')) >= current_date

Current_date is a special register that returns the current date, but that’s not important right now.

The date conversion part involves several nested functions to get to a final date, so here’s the breakdown using a date of 1st September 2015 (1150901):

• digits(STDT) converts the 7 digit number into a 7 character string. So 1150901 is converted to ‘1150901’.
• The IBM i can figure out which century it’s in by looking at the year, so I don’t need the century flag and the substr(digits(STDT), 2, 6) strips it out to give me a value of ‘150901’
• The timestamp_format function takes the date string and uses the format string of ‘YYMMDD’ to generate a timestamp of 2015-09-01-00.00.00.000000. Since I only passed it a date, the hours, minutes and seconds are all zeroes.
• And finally, I can use the date function to retrieve the date from the generated timestamp.

And here’s the result:

CTNR      DATE      DATE
C1000001  01/09/15  31/08/16

Pretty, and portable.