Jonathan Snook has a quick tip for PHPers out there using MySQL and looking for an easy way to concatinate a lot of data in your queries.
This is just a quick tip. If you have a bunch of data that you need to concatenate, take a look at MySQL's GROUP_CONCAT function.
For example, way back when, I wrote about (and subsequently weighting those tags) to an application. It was a very simple approach with each record having a tags field. It was just a simple text field and I stored all the tags with spaces. However, to pull out a list of all tags being used in the system, I returned the tags field from all records, looped through each record, exploding the tags onto an array.
Using the group_concat() function already in MySQL, he was able to reduce looping through his data, splitting on the spaces down to a single line call in SQL telling it to concatinate spaces. He includes the code (just a few lines) to get the job done.