ID design

We often take the IDs that we use in databases and applications for granted. As long as we can identify a data record with a unique number, everything is great. Recently, I ran into an interesting problem in an existing application. The ID that was used has this format:

ABBBCCC

A = last digit of year
BBB = day number of the year
CCC = sequence number

For example, you could get on 2 february 2009 this ID: 9033012. This would be the twelveth data record of the day.

More digits

Sometimes, the application would generate more than 1000 data records on a day and run out of numbers. In that case the application just add digits to get something like this:

ABBBCCCDDD

A = last digit of year
BBB = day number of the year
CCCDDD = sequence number with additional digits

Example: 9003123456

Perhaps you can sense some trouble here...