ISO Week and Year in PHP and PostgreSQL

The new year always brings with it a few small things that go bump in the morning. 2008 was no different. Intervals started behaving oddly on New Year’s Eve morning — the default timesheet was a year behind schedule. What happened?

In our PHP code, we are using the ISO-8601 week number of year, as specified on the PHP date function page, but we weren’t using ISO-8601 for the year. The ISO-8601 week number specifies the last monday of a year as the first week of the new year, if that new year begins before thursday. Intervals thought it was the first year of 2007!

In PHP, the fix was as easy as converting all instances of date(‘Y’) to date(‘o’), according to

ISO-8601 year number. This has the same value as Y, except that if the ISO week number (W) belongs to the previous or next year, that year is used instead. (added in PHP 5.1.0)

That fixed everything on the PHP side of things. But next we had to dig into the SQL queries and get them to use the ISO Year.


PostgreSQL 8.2.5 doesn’t support ISO Year in the Extract function. EXTRACT(ISOYEAR, timestamp) is being included in PostgreSQL 8.3, as specified here in the RC1 documentation. But PostgreSQL 8.3 hasn’t been released yet, and we needed to fix things immediately.

Our final PostgreSQL fix was to instead use the TO_CHAR(timestamp, ‘IYYY’) function. It’s not ideal to be using a string formatting function for data comparisons, because it slows down some of the queries. But we had to trade some performance to get things working properly again in the new year. As soon as the PostgreSQL developers release a stable version of 8.3, we’ll change our queries back to using EXTRACT(ISOYEAR, timestamp).

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2 Responses to “ISO Week and Year in PHP and PostgreSQL”

  1. Michael Says:

    Looks like 8.3 should be snappier as well.

  2. Online Time Tracking, Task Management and Project Management, Reprised | Project management and time tracking blog for web designers and small business :: the Intervals Blog by Pelago Says:

    Kramer auto Pingback[...] ISO Week and Year in PHP and PostgreSQL Pelago :: web design, web development blog ::  January 20th, 2010 @ 3:07 am [...]

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