Why A Table of Dates?

I thought it would be nice to build on the numbers table with another very useful tool.

Dates are pretty important–especially if you are playing with data warehousing. Not only dates, but all the different properties and derived goodies contained within them. You really don’t need a dates table, unless you care about efficiency and getting to all the good stuff quickly. Perhaps I’ll showcase some of the “goodies” in later posts.

Sure, most databases have built-in functions to get everything you might want. But do you really want all the inefficiency that comes with calling functions and doing calculations over and over again? I hope not. I used the method in this article when I developed a SQL Server data warehouse for a company I worked for. It was adopted by our other SQL Server guru for all the date-sensitive stuff we did (which was a lot). It increased efficiency by leaps and …

Making The Numbers Table Useful

It’s not easy to find a solution to a very simple problem in MySQL: converting a comma separated list of values into rows. Oracle database users find gobs of tutorials on using REGEXP and CONNECT BY LEVEL to make this happen. MySQL doesn’t have that. So, use the numbers table from the previous post!

The transposing is made possible by (ab)using the SUBSTRING_INDEX function. I love this function. It is right up there with GROUP_CONCAT when mixing NULL and non-null strings.

I will be using comma separated values. You can use any delimiter character you like.

Bonus: This works with empty strings, strings with one value only, and empty delimiters (i.e. “my value,,previous is empty”). No extra code needed.

Making Magic Happen

SET @mycsv = …

Why You Care About Numbers

I have worked a bit with Oracle. As such, I hang out around Oracle developers. There seems to be a common complaint among our kind when it comes to MySQL–”There aren’t any sequences!”

It never really bothered me. I wasn’t always an Oracle guy, so I didn’t always have sequences. I’m the kind of person who likes to experiment and make things happen. It just so happens there is a nice tool to help with this perceived absence: the “numbers table.”

It is really easy to set up. And, regardless of your database background, I think you will grow to love your utility.

There are multiple ways to achieve the result you want. For me, the easiest way is to work with decimal numbers. Why? Because that’s how we think. That’s pretty much standard for humans. Yeah, I know. Geeks think hexadecimal. Let’s not go there.

Without further ado, here is how you can create …

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