Writing MySQL functions in C
Andreas Jansson | 15 December 2010
In the previous post Zdenek explained how to use MySQL stored functions to calculate the distance between two points on the lat/lng plane. Here I take his function as a starting point to describe how to implement user defined functions written in C, and import them into MySQL.
User defined functions (UDF) are compiled C functions that you can use as normal functions within MySQL. UDFs have a number of advantages over stored functions written using SQL, the most important being improved performance and the fact that you can use them as aggregate functions (like you can with SUM(), AVG(), etc.).
Writing UDFs is easy. So is compiling and importing UDFs into MySQL. First you need to do a little bit of setting up. This is how you do it (in Ubuntu and Red Hat).
Automatic geolocation and SQL
Zdenek Machek | 16 November 2010
Recently we launched a website and platform for iGo Gift Vouchers. One of the screens shows an interactive list of the shops where vouchers can be used. The classic interface design pattern for this is to ask users to provide a postcode, or the name of a city or town, and then display the shops in that area on a map.
As usual, we decided to try something new and improve a little on the traditional functionality. We wanted to automatically detect where the user is right now, so we can display shops in their area as soon as they arrive on the page, without them having to enter any information. You can see how it works at www.igogiftvouchers.co.uk/myigo - when your browser asks if you would like to share your location with the page, just click the option to accept.
So why Geolocation and SQL? The first part of this task, identifying where the user is, is handled on the client side usining JavaScript. But SQL comes in as the best and fastest tool for the second part of the task: identifying which shops are nearest and should be displayed on the map.
