Descriptive statistics can be quite useful for simple analysis of records in a database. For example, to calculate average numbers of sales or products for a particular duration, or the Variance of sales for a month etc. We can easily calculate standard descriptive statistic measures in MySQL such as MEAN, SUM, STANDARD DEVIATION, VARIANCE, MIN and MAX using built-in functions.

He includes both the SQL and a bit of PHP code showing how to get these statistics (based on a simple data set of student scores). The PHP is required to more correctly evaluate the median and mode values as it's easier to evaluate those in PHP.

Link: http://www.codediesel.com/data/calculating-descriptive-statistics-in-mysql]]>The start of this new year started with some buzz about a leap second being introduced between Dec 31st 2008, 23:59:59 and Jan 1st 2009, 00:00:00. I've had people ask where this leap second actually comes from, and whether you need to worry about it in your applications. To understand leap seconds means, unfortunately, understanding how time is actually kept.

He ponints out one of the major problems - how time is kept. With variants of Universal Time, it makes it hard to track down what's "right". He breaks out the difference between other time storage methods and the unix time that PHP can use (that counts the number of seconds since Jan 1st 1970) and how the leap second was handled for each.

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