MySQL custom primary key generator

Question

I have written an invoice module for our reservation system.

So when I create a new invoice, I automatically generate a primary key through MySQL.

However for th

Answer 1

A warning against naive year/week like 2012/01. YEAR(NOW()) being wrong.

Better use YEARWEEK(NOW()). Gives a number like 201201

The following shows that year is not necessarily year-of-week-number:

mysql> SELECT YEARWEEK('1987-01-01');
       -> 198652

For the rest having year and week in one single int, is in fact simpler.

int year = yearweek / 100;
int week = yearweek % 100;