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Curated SQL Posts

So You’ve Got Database Corruption—Now What?

Published 2018-07-25 by Kevin Feasel

Jeff Mlakar walks us through troubleshooting an instance of database corruption:

Before we dive into fixing database corruption it is important to know what not to do. There are things we can do which will make a bad situation even worse.

  1. Don’t Panic – most sysadmins are used to having their cages rattled and can keep cool under duress. Jumping to action without a plan is not wise. Now is not the time to start trying things and performing thoughtless actions.

  2. Do NOT Detach the Database – we may never get it back again as it may be in a recovery pending state.

  3. No restarting SQL Services – databases may never get started up again just like the above.

  4. Don’t Reboot the Machine – same as above 2 points

  5. Don’t Start by Trying to Repair the Corruption – root cause analysis is critical to preventative measures

Jeff then walks us through things that he does to discern the root cause and correct the issue (if possible).

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Building OData Sources In Biml

Published 2018-07-25 by Kevin Feasel

Cathrine Wilhelmsen gives us a workaround for no native OData support in Biml:

As of July 2018, there is no built-in Biml support for OData. To work with OData in Biml, you have to create a custom source and connection manager. This requires more Biml code than built-in functions like OleDbSource and may look a little overwhelming at first. But don’t worry! You don’t have to start from scratch.

In this blog post, we will first look at the properties of the OData Connection Manager and how to script it in Biml. Then, we will do the same for the OData Source. Finally, we will tie it all together and create a complete SSIS package that you can use a starting point for your own projects.

There’s a quick and easy solution but definitely read the whole thing to catch any oddities which might arise from reverse engineering your SSIS packages.

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Power BI And Many-To-Many Joins

Published 2018-07-25 by Kevin Feasel

Teo Lachev notes a big improvement to Power BI’s data modeling story:

The July 2018 preview of Power BI Desktop delivers two killer preview features that solidify the Power BI position as the best data modeling tool on the market. First, Microsoft relaxes the Power BI relationship limitations by letting you create M:M joins between two tables. Second, you can now create a composite (hybrid) data model with different storage modes, such as from an SQL Server database configured for DirectQuery and from an imported text file. Without reiterating the documentation, here are some important notes to keep in mind based on my pre-release testing.

But read the whole thing, which includes some limitations around hybrid data models.

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Parsing Power BI Logs With Power BI

Published 2018-07-25 by Kevin Feasel

Kellyn Pot’vin-Gorman uses Power BI to analyze Power BI logs for issues:

Do I really want to go through all this data by hand?  BI is a reporting tool, so what if I bring them into Power BI?  Let’s start with the first MS Mashup Container log-

In Power BI, click on Get Data –> Text and change the file type to “All Files” in the explorer and go to the directory that contains the trace files:

C:\Users\<user>\AppData\Local\Microsoft\Power BI Desktop\Traces\Performance

Remember that you will need to have “hidden items” set to be displayed to browse down to this folder.  Choose the files you wish to load in the directory and Power BI and choose a Customer delimiter of a quotes, (“) to separate the file.  This will load a file that will have a few columns you’ll need to remove that contain data like colons, nulls and other syntax from the file

I like it.

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CXCONSUMER Not Entirely Harmless

Published 2018-07-25 by Kevin Feasel

Erik Darling points out a case where CXCONSUMER waits are important:

In this sample there are absolutely no waits whatsoever on CXPACKET.

They are nonexistent.

If you were hoping to find out that they were way crazy out of control call a priest and ditch your bar tab we’re driving on the train tracks, you’ll be awfully disappointed.

There just aren’t any.

There’s only one core in use for nearly the entire duration, aside from some blips.

That’s disappointing.  I was hoping to be able to ignore this wait altogether.

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The Value Of CROSS APPLY

Published 2018-07-25 by Kevin Feasel

Kendra Little talks about one of my favorite T-SQL operators:

Here’s my top 3 favorite uses for CROSS APPLY and OUTER APPLY:

  1. APPLY is fantastic for calling table valued functions. I didn’t include questions about those in the quiz, simply for the purposes of keeping the code simple, and because I wanted the quiz to be about thinking through how apply works — but it’s still the #1 use.

  2. Another thing I might use it for is when a query needs a correlated subquery — somewhat like an inline function.

  3. And I also like it for queries that have a calculation that needs to be done and which is referenced in multiple columns in the query, or perhaps also in a predicate and the select. You can perform the computation once in the apply and then reference it multiple times. That way if you have to change the formula later on, you only have to change it in once place, plus I find it’s easier to read in some cases.

Item number three is something I learned from an older blog post Kendra wrote and regularly use APPLY for this purpose.

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Using Azure Data Lake Analytics With Integration Services

Published 2018-07-24 by Kevin Feasel

Yanan Cai announces that Azure Data Lake Analytics has a new task in the Azure Feature Pack for SQL Server Integration Services:

With ADLA Task in Azure Feature Pack, you can now orchestrate and create U-SQL jobs as a part of the SSIS workflow to process big data in the cloud. As ADLA is a serverless analytics service, you don’t need to worry about cluster creation and initialization, all you need is an ADLA account to start your analytics.

You can get the U-SQL script from different places by using SSIS built-in functions. You can:

  • Edit the inline U-SQL script in ADLA Task to call table valued functions and stored procedures in your U-SQL databases.

  • Use the U-SQL files stored in ADLS or Azure Blob Storage by leveraging Azure Data Lake Store File System Task and Azure Blob Download Task.

  • Use the U-SQL files from local file directly using SSIS File Connection Manager.

  • Use an SSIS variable that contains the U-SQL statements. You can also use SSIS expression to generate the U-SQL statements dynamically.

Read on for more information and a link to download the pack.

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Generating Basic Features From Text Data In R With textfeatures

Published 2018-07-24 by Kevin Feasel

Abdul Majed Raja demonstrates the textfeatures package in R:

Michael Kearney, Assistant Professor in University of Missouri, well known in the R community for the modern twitter package rtweet, has come up with a new R packaged called textfeatures that basically generates a bunch of features for any text data that you supply. Before you dream of Deep Learning based Package for Automated Text Feature Engineering, This isn’t that. This uses very simple Text Analysis principles and generates features like Number of Upper Case letters, Number of Punctuations – plain simple stuff and nothing fancy but pretty useful ones.

It’s a start for text analysis, though there’s a lot more after this.

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SSIS: Target Server Version Leads To Script Task “Corruption”

Published 2018-07-24 by Kevin Feasel

Slava Murygin walks us through an ugly-looking error with an easy fix:

There are probably a lot of SSIS corruption errors, but that is one that is very easy to solve.
The whole error message is texted like this:

Script Task:Error: The Script Task is corrupted.
Script Task:Error: There were errors during task validation.
Script Task:Error: There was an exception while loading Script Task from XML: System.Exception: The Script Task “ST_74aca886806a416fa34ae89cac6237c2” uses version 15.0 script that is not supported in this release of Integration Services. To run the package, use the Script Task to create a new VSTA script. In most cases, scripts are converted automatically to use a supported version, when you open a SQL Server Integration Services package in %SQL_PRODUCT_SHORT_NAME% Integration Services. at Microsoft.SqlServer.Dts.Tasks.ScriptTask.ScriptTask.LoadFromXML(XmlElement elemProj, IDTSInfoEvents events)

That error came from an execution of SSIS package and it points that particular Script task is corrupted.
It is very confusing, because if you try to run the same package in the Visual Studio everything will be fine:

I’d consider the initial error that “The Script Task is corrupted.” to be a bad error message.  The longer description is helpful and explains the problem, but the word “corruption” has a certain scary connotation to DBAs and tossing it around when you really mean to say “Fix your target version” is unhelpful.

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Getting A Random Row From A Small Data Set

Published 2018-07-24 by Kevin Feasel

David Fowler has a quick script to get a random row from a relatively small table:

A couple of times recently I’ve seen the question asked, ‘How can I select a single row at random from a table?’.

There are often a few ways of doing this suggested, most seem to rely using CTEs or temp tables.  I thought I’d share, in a quick post a very simple and easy way of doing it that I’ve used a couple of times.

The script David provides requires a table scan, so it doesn’t scale out very well.  But depending on your hardware, that can still be pretty efficient into the tens of thousands of rows.

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