Tableau Data Sources: Live vs Extract

Continuing last-week’s trend, we’ll again take a look at an aspect of Tableau that people often find confusing: the difference between live and extracted data sources. And again, we’re going to take a bit of a database perspective to clarify the situation.

The impetus for this post is a number of statements I’ve seen along the lines of:

A live data source is just a real-time extract of your data.

This is my favorite kind of wrong: subtly wrong.

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Dimensions and Measures: A SQL Perspecitive

I thought I’d kick this off gently. I remember going through Boot Camp after joining Tableau and learning about dimensions and measures. And I remember finding the descriptions rather confusing.

I don’t recall the precise phrasing, but it went something like this:

Dimensions are usually those fields that cannot be aggregated; measures, as its [sic] name suggests, are those fields that can be measured, aggregated, or used for mathematical operations.

Or this:

Measures are the result of a business process event… Dimensions are reference variables that give context to measures.

I don’t really mean to criticize these definitions, but to a database guy, they seem rather imprecise. For someone with a little SQL know-how, the actual definition is both crisp and helpful in understanding what Tableau really does under the covers—this helps predict what actions in the UI will do, so you don’t just blindly drag-and-drop until things look right.

The rest of this post is a crisp explanation of dimensions and measures for someone who knows a little SQL.

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Hello World!

It’s really: “Hello again!”

A long time ago in a job not so far away, I kept a blog over at MSDN. Back then, I was a new program manager in SQL Server, and that blog really caught it’s wind as we were pulling together SQL Server’s geospatial support. After I left that project, things just sort of trailed off.

Over the years, I’ve considered starting up a blog again, but I’ve struggled to come up with a theme that was coherent, current, and that I could actually write about publicly.

But recently, I’ve started to think this is too high a bar. My goal with this new blog is merely to write a weekly post on something interesting to me. It’s selfish, but I hope you find it interesting enough to read along.

So buckle up—it might get bumpy.

And welcome!