Blog Post

Derby City Data Days


It was awesome to see the Kentucky data community come out for the first Derby City Data Days in Louisville, KY! Bringing together communities from Ohio, Tennessee, and Kentucky, the Derby City Data Days event was an excellent follow-up to Data Tune in March and deepened relationships and networks made at the Nashville event. In case you missed it, below are my notes from the sessions I attended as well as the resources for my session. Be sure to check out these speakers if you see them speaking at a conference near you!

Building Self-Service Data Models in Power BI by John Ecken

What and why: we need to get out of the way of business insights. If you try to build one size fits all, it fits none. Make sure you keep your data models simple and streamlined.

Security is paramount to a self-service data model. RLS is a great option so folks only see their own data. You can provide access to the underlying data model for read and build which enables them to create their own reports off the data they have access to. If you give your user contributor access, then RLS will go away for that user. Keep in mind, business users need pro license OR need to be in a premium workspace.

One really great option is for people to use the analyze in Excel option to interact with the most popular BI tool – Excel. This allows them to build pivot tables that can refresh whenever needed. You can also directly connect to Power BI datasets from their organization! You can set up the display field option as well to get information about the record you connect to. Pretty slick! With this, security still applies from RLS which is awesome.

Data modeling basics – clean up your model by hiding or removing unnecessary columns (ie sorting columns). Relationships matter. Configure your data types intentionally. Appropriate naming is vital to business user success. Keep in mind where to do your transformations – SQL vs DAX (think Roche’s Maxum). Be sure to default your aggregations logically as well (year shouldn’t be summed up).

Power BI Measures – creations, quick create, measure context, time-based functions. Whenever possible, make explicit measures (using DAX) and hide the column that it was created off of so people utilize the measure you intended. Make sure you add descriptions, synonyms (for Copilot and QA), featured tables, and folders of measures. The functionality of featured tables makes it wise to use folders of measures within your fact tables.

John likes to use LOOKUP to pull dims back into the fact table so he ends up with as few tables as possible. There are drawbacks to this such as slower performance and model bloat, but the goal is for end users who don’t have data modeling experience or understanding. Not sure I agree with this method since it’s not scalable at all and destroys the purpose of a data model. Make sure you hide columns you don’t want end users to interact with.

To turn on feature table, go to the model view then go to Properties pane and toggle that is featured table button. It will require a description, the label that will populate, and the key column (cannot be hidden) that the user will put in excel as a reference for the business user to call records off of.

The PIVOT() TSQL Operations by Jeff Foushee


Be sure to look at his GitHub for the awesome source code!

Come to Lousiville on May 9th to see a presentation on JSON and TSQL.

The goal of this is to avoid FULL OUTER JOINs. This is extremely unscalable since maintenance would be terrible. We will avoid this by using pivot. Pivot means less rows, more columns. PIVOT promotes data to column headers.

You get to decide how the tuple that’s created on the pivot is aggregated (count, min, max, sum, avg, etc.). Exactly one aggregate can be applied, one column can be aggregates, and one columns values can be promoted into the column header.

PIVOT ( SUM(Col1) FOR [ID] IN ([ID_value_1], [ID_value_2], etc.)
SUM = the aggregate, ID = the column that will become more columns, the IN values = the column values from ID that will be promoted into the column header.

Time for a 3 column pivot. For this, we are doing a two column pivot and ignoring one of the fields. You can even pivot on computed fields but make sure you include the values in that inclusion clause. Be careful about adding unnecessary data.

How do you manage the VTCs (the column values that end up as column headers)? Option 1 – don’t. Option 2 – explicitly request the ones of interest and provision for future extras. Option 3 – use dynamic SQL! You can use cursor, XML, etc. Check out his ppt deck from github for code samples!

An n-column PIVOT works by essentially creating a 2-column pivot (at the end of the day it’s only two columns that ever get pivoted) and knowing which you want split into new columns.

Ugly side of PIVOT = lookups. The more fields you need to add in from additional tables, the worse performance will be. Your best option there would be to do a group by, the pivot. Another limitation is you can’t use a function in your pivot aggregation (SUM() vs SUM() *10). Get your raw data clean then pivot.

Time for UNPIVOT!

Unpivot = convert horizontal data to vertical. Less columns, more rows. Unpivot demotes column headers back into data.

Be very very careful with your data type your about to create. Remember lowest common denominator, all the values must be able to fit in one common datatype without overflow, truncation, or collation.

UNPIVOT( newColPropertyValue FOR newColPropertyName IN ([originalCol1], [originalCol2],etc.)

You need to make sure all your original columns have the same datatype. NULLs get automatically dropped out. If they are needed, you can convert them using an ISNULL function to a string value or int value depending on your need.

There’s also an option for XML-based unpivot.

Cross Apply = acquires a subset of data for each row found by the outer query. Behaves like an inner join, if no subset is found then the outer row disappears from the result set. Outer Apply is similar but it’s more like a left join. Cross Apply does keep your NULL values. You can also use a STRING_SPLIT with cross apply.

Multi-Unpivot normalizes hard-core denormalized data. You just add more UNPIVOT lines after your initial FROM statement! Make sure you have a WHERE statement to drop any records that don’t align at a column level. Something like WHERE LEFT(element1,8) = LEFT(element2, 8).

My Session – Time for Power BI To Git CI/CD

Thanks to everyone that attended my session! Had some great questions and conversations! Here’s the link to my github with the slide deck from today:

Medallion Architecture for Fabric by Steve Hughes

This session was awesome! We were able to watch a series of Fabric 5 minute videos and had an amazing discussion between them about options for building out a Fabric infrastructure using medallion techniques. Check out Steve’s YouTube channel for his Fabric 5 playlist and to learn more about his experience working with ALS.

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