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The serendipity cache blew up on me for this article so I had to split it into 2 parts.

DATE_ADD to the rescue

MySQL knows how to work with the Gregorian calender, and I believe it is easier to let MySQL do the work, rather than trying to figure out how to implement the different cases. I chose to implement the "last day of the month" technique. In this case, we'll do this by creating a mysql date based on March 1st of the current year, and subtract one day from it to get to the last day of February.

If you read my article on "Finding next monday" using mysql date functions, you would have seen how DATE_ADD() can be used to help solve a lot of problems, even though the name can be misleading when you are actually using it to subtract. Using it with the following test dates proves that mysql has fully implemented the leap year logic accurately:

Continue reading "Calculate a person's age in a MySQL query -- continued"

Recently a question was posed on the Phpfreaks.com forums, as to the best way for someone to store a user's birth date using the MySQL database. One person suggested using a varchar as they were most familiar with string functions. My answer was to use the MySQL date type.

I provided a quick "advantages of using date" comparison list:
Storing as a DATE
•A MySQL Date requires 3 Bytes of storage
•You can do Date arithmetic inside mysql (search for dates within ranges) and use mysql functions to calculate values directly in a query
•It intrinsically will only store valid dates
•You can format it in numerous ways

Storing as a Varchar
•A string will require minimum 8 bytes, or 10 with separators
•can't do any form of efficient native range queries
•can't reformat it easily in SQL
•will allow completely invalid dates

I thought a great proof of the benefit of this approach was to show that you could have MySQL calculate the person's current age in a query, using their birthday. Certainly with a string, using PHP for example, you would typically query the database to pull out the string and for each row, turn it into a PHP date and do some calculations in your code, and you'd arrive at the same place, but I wanted to show just how capable SQL -- and in this case MySQL can be especially when you use the native data types and some functions.
Continue reading "Calculate a person's age in a MySQL query"