Normalize

I walk through a scenario which underscores the importance of normalization:

This joins my records to a tally table, which gives one row for each character in RemovedValue (that is, the numbers without recordset separators).  I then retain only the values which start a sequence, and use SUBSTRING to snatch up four digits. What I’m left with is a column named SplitVersion, which has one row for each customer, campaign, and 4-digit value (which is equivalent to my normalized table’s structure).

If that wasn’t exciting enough, we now need to slam this back together into our denormalized format, and that’s what tallyjoin does. It uses the FOR XML PATH trick to concatenate my four-digit values into one string, separated by commas. You might be wondering why I use comma instead of CHAR(30), and the answer is that converting CHAR(30) to XML returns a nasty result, so instead of trying to handle that, I use a character which is copacetic and translate it back using the REPLACE function after casting my “XML” result to varchar.

The implicit story here is, you can find someone who knows how to use tally tables, how to concatenate strings of data (quickly!), who knows how to tie various pieces of the puzzle together, and so on…or design the database the right way and avoid this pain later.

Anchor Modeling

Steph Locke has a presentation on Anchor Modeling as 6th Normal Form:

Anchor Modelling moves you beyond third normal form and into sixth normal form. What does this mean? Essentially it means that an attribute is stored independently against the key, not in a big table with other attributes. This means you can easily store metadata about that attribute and do full change tracking with ease. The historical problem with this methodology is that it makes writing queries a real pain. Anchor Modelling overcomes this by providing views that combine all the attribute data together.

Anchor Modeling is a rather different approach, so if it sounds interesting, check out the tutorial.

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February 2017
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