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Month: July 2019

SQL Graph and Hierarchies

Published 2019-07-16 by Kevin Feasel

Hasan Savran shows how you can use SQL Server graph tables to handle hierarchical data:

The > determines the direction of the query. By changing this arrow into other direction, you can use the same relation table to find who manages employee. For example, let’s rewrite this query and look who manages East Manager

SELECT emp.Name as Emp, emp2.Name as Mgr
FROM Hr as emp, ReportsTo as r, Hr as emp2 
WHERE MATCH(emp<-(r)-emp2) and emp.empid = 8

There are a few relational approaches which work well for hierarchies, though they all come with tradeoffs in terms of read complexity, write complexity, and development complexity. Click through for Hasan’s take on the graph-based approach.

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Powershell and Windows Terminal Profiles

Published 2019-07-16 by Kevin Feasel

Jeffery Hicks shows how you can modify your Windows Terminal profile using Powershell:

I recently updated my Windows 10 systems to the 1903 release. One of the reasons is that I wanted to try out the new Windows Terminal preview. You can find it in the Windows Store. This is bleeding edge stuff and far from complete but promises to a great addition. Now you will be able to have all your command terminals, in one tabbed application and easily be able to switch between them. As I said, this is far from being a finished and polished product. Right now, if you want to add a new profile, that is another terminal, you have to manually edit a json file. If you have VS Code installed, the file will open in that.  Otherwise, I’m assuming you’ll get whatever application is associated with the .json extension.

Read on for a Powershell one-liner which lets you create a terminal profile.

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How .NET Code Talks to Spark

Published 2019-07-15 by Kevin Feasel

Ed Elliott has a great diagram showing how user-written .NET code communicates with Spark over the Java VM:

4. Spark-dotnet Java driver listens on tcp port
The spark-dotnet Java driver listens on a TCP socket. This socket is used to communicate between the Java VM and the dotnet code, the dotnet code doesn’t run in the Java VM but is in a separate process communitcating with the Java VM via that TCP postrt. The year is 2019, we serialize and deserialize data all the time and don’t even know it, hell notepad probably even does it.

It’s serialization & deserialization as well as TCP sockets all the way down.

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A Quick Keras Example

Published 2019-07-15 by Kevin Feasel

Shubham Dangare takes us through a quick example using Keras and TensorFlow in Python:

Keras is a high-level neural networks API, written in Python and capable of running on top of Tensorflow, CNTK  or Theano. It was developed with a focus on enabling fast experimentation. In this blog, we are going to cover one small case study for fashion mnist.

Fashion-MNIST is a dataset of Zalando’s article images—consisting of a training set of 60,000 examples and a test set of 10,000 examples. Each example is a 28×28 grayscale image, associated with a label from 10 classes. Zalando intends Fashion-MNIST to serve as a direct drop-in replacement for the original MNIST dataset for benchmarking machine learning algorithms. It shares the same image size and structure of training and testing splits.

The end result wasn’t that great, but Shubham was using a sequential model rather than a convolutional neural network, so you can probably take this as a starting point and improve upon it.

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Diving Into Clustered Index Seeks

Published 2019-07-15 by Kevin Feasel

Hugo Kornelis looks in detail at the clustered index seek:

The Clustered Index Seek operator uses the structure of a clustered index to efficiently find either single rows (singleton seek) or specific subsets of rows (range seek). Because a clustered index always contains all columns in a table, a Clustered Index Seek is one of the most efficient ways for SQL Server to find single rows or small ranges, provided there is a filter that can be used efficiently.

The behavior of the Clustered Index Seek operator is in fact exactly the same as the behavior of the Index Seek operator, with only a very few differences as noted below. Though these two operators do have different names, not only in the graphical execution plan but also in the underlying XML, I suspect that in reality they are both using the same internal logic and not a copy of it.

Read the whole thing.

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SentryOne Plan Explorer in Azure Data Studio

Published 2019-07-15 by Kevin Feasel

Aaron Bertrand gives us the behind-the-scenes look at SentryOne’s Plan Explorer extension for Azure Data Studio:

Like the desktop application, the Plan Explorer extension is designed to provide you with richer graphical execution plans for your real-time queries against SQL Server. It is based on a modest subset of functionality; we’ve started with just the plan diagram, a basic statements grid, tooltips, and access to the XML (so you can open the plan in other tools). We will add more features to the extension over time to try to get you as close to full parity with the desktop client as possible.

I gave it a quick try this weekend and had to pop XML results into the desktop client to get what I really wanted to see, but I’m excited over what this looks like medium-term.

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Power BI Pareto Charts

Published 2019-07-15 by Kevin Feasel

Matt Allington shows how you can build up a Pareto chart in Power BI:

Pareto Analysis is a statistical technique that applies the Pareto Principle to data. This is more commonly known as the 80:20 Rule. The Pareto Principle is based on the presumption that a relatively small number of inputs (20%)  have most impact on the results/output (80%).  The 80:20 rule can be applied to a wide variety of data in most businesses. 

Examples include:
– Which 20% of products make up 80% of sales
– Which 20% of customers make up 80% of profit.

Pareto analysis is a rule-of-thumb technique but it does provide reasonably useful results much of the time.

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Finding Gaps in Dates

Published 2019-07-15 by Kevin Feasel

Jason Brimhall shows how you can find gaps in your data:

This method is the much maligned recursive CTE method. In my testing it runs consistently faster with a lower memory grant but does cause a bit more IO to be performed. Some trade-off to be considered there. Both queries are returning the desired data-set which happens to be my missing question days. Only, I have added an extra output in the second query to let me know the day of the week that the missing question occurred on. Maybe I forgot to enter it because it was a weekend day or maybe I opted to not create one at all because the day lands on a Holiday. Let’s take a small peek at the results.

This is a good use for tally tables (or for a calendar table, which is basically a date dimension called something else so you can feel comfortable dropping in a non-warehouse system).

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Azure SQL Database Hyperscale

Published 2019-07-15 by Kevin Feasel

Jeroen ter Heerdt explains the basics behind Azure SQL Database Hyperscale:

Connecting to your Hyperscale database is exactly the same as any other Azure SQL or SQL Server database – for example, you can use SQL Server Management Studio or Azure Data Studio. That is the exactly point. Hyperscale provides capabilities not found in other cloud databases such as scale and query performance, but it has no impact on your applications. If you do an in-place migration of a SQL database that is already on another service tier to Hyperscale, the connection string would not even change. Your application does not have to be changed and it will benefit from bigger scale and improved query performance. And who does not like the extra scale and query performance? 

This post covers the basics of database creation but does not go much further into it than that. Jeroen does promise a multi-part series, however.

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When Values Disappear in Power BI

Published 2019-07-15 by Kevin Feasel

Chris Webb explains what happens when a selected value on a slicer disappears in the underlying data set in Power BI:

There is a slicer on the left with five items in it, a table showing the actual contents of the table (I’ve disabled visual interactions so the slicer doesn’t slice the table) with five rows and a card showing the output of the following measure:

Selected Number = SELECTEDVALUE(MyNumbers[Column1], "Nothing Selected")

In the screenshot above you can see I have selected the value 78 in the slicer and the measure – as you would expect – displays that value.

Now what happens when you refresh the dataset and the table contains a different set of numbers? 

Read on for the full explanation.

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