Analysis Services Query Analyzer

Last week a new, free tool for analysing the performance of MDX queries on SSAS Multidimensional was released: Analysis Services Query Analyzer. You can get all the details and download it here:

https://ssasqueryanalyzer.github.io/

…and here’s a post on LinkedIn by one of the authors, Francesco De Chirico, explaining why he decided to build it:

https://www.linkedin.com/pulse/asqa-10-released-francesco-de-chirico/

I’ve played around with it a bit and I’m very impressed – it’s a really sophisticated and powerful tool, and one I’m going to spend some time learning because I’m sure it will be very useful to me. It’s an AddIn for SQL Server Management Studio and captures Profiler and Perfmon data for an MDX query when you run it, does so for a cold and warm cache, and then displays the results in a variety of graphs and charts. And it even has an MDX formatter built in!

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You can find a full list of features here, and when you download the tool it comes with very detailed documentation. Definitely a must-have for all serious SSAS Multidimensional developers.

Running M Queries In Visual Studio With The Power Query SDK

Writing M in the Advanced Editor in Excel or Power BI can be a frustrating experience unless you’re the kind of masochist who loves writing code in Notepad. There are some options for writing M code outside Excel and Power BI, for example Lars Schreiber’s M extension for Notepad++ (see here for details) or the M extension for Visual Studio Code (available from the Visual Studio Marketplace here; more details on Brett Powell’s blog here), but the trouble with them is that you have to copy the code back into Excel or Power BI to run it. What many people don’t realise, however, is that it is possible to write M code and have IntelliSense, formatting, keyword highlighting and also the ability to execute your own M queries, using the Power Query SDK in Visual Studio.

The Power Query SDK (which you can download here) supports Visual Studio 2015 and 2017 and is intended for people who are writing custom Data Connectors for Power BI. To let you test your Data Connector you can create a .pq file containing M code, and this in fact allows you to run any M query you want whether you’re building a Data Connector or not.

Here’s how. First, install the Power Query SDK and then open Visual Studio and create a new project. Find the Power Query template, select the PQ file option and give your file a name:

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Then, in the .pq file that is created, you can enter an M query and then either press the Start button on the toolbar or hit F5 to run the query. The output of the query is shown on the Output tab in the M Query Output window:

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Right-clicking on your project in the Solution Explorer pane and selecting Properties brings up a Properties dialog with various properties that control how your queries behave:

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Many of the properties are self-explanatory, at least for anyone used to writing M in Power BI or Excel. FastCombine turns off data privacy checks. Allow Native Query lets you use M queries that contain ‘native’ queries (for example your own SQL queries if you’re using a SQL Server data source), as Cédric Charlier shows here. A few of them, such as Legacy Redirects, I have no idea about yet (I should really ask someone…). Turning on Show Engine Traces displays engine trace information in the Log tab of the M Query Output pane; turning on Show User Traces displays trace information generated by the use of the Diagnostics.Trace() function in your code in the Log tab. You can save the contents of the Log tab to a text file.

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Error messages are displayed on the Errors tab of the M Query Output pane:

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When you have a query that connects to an external data source, the first time you try to run your query you will be prompted to set the credentials used to connect to that data source (as you would in Power BI Desktop), and the data privacy level for the data source, on the Errors pane:

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The query won’t actually run this first time though; you’ll need to hit Start/F5 again to see the results. If you close the project and then reopen it you will need to enter credentials again; alternatively, on the Credentials tab you can save the credentials used for a data source to a .crd file which can then be reloaded when you reopen your project. You can also edit and delete credentials on the Credentials tab.

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If I’m honest it’s all very basic but it does the job. The main thing that I miss from writing M code in Power BI is the Query Editor UI – when I write M code there I only write about 50% of it manually, the rest I generate by clicking buttons in the UI because it’s faster. Give me the Query Editor (or the ribbonless version of it that comes with SSDT, because Visual Studio doesn’t support ribbons apparently) and I’ll be happy. Even better, give me the improved code editing functionality in the Advanced Editor in Power BI Desktop and Excel that we’ve been promised!

Creating Excel “Data Dump” Reports From Power BI

We’ve all met them: the users whose idea of a ‘report’ is a large table of data dumped into Excel. However many beautiful data visualisations they see, however many times you try to convince them of the benefits of using Power BI to build reports, they just want to know where the “Export to Excel” button is so they can carry on analysing data in the same old way. Sometimes there’s a valid reason for doing this, sometimes not, but all too often internal politics means that you have to accommodate them.

If you’re using Power BI the obvious way to do this is to use the “Export Data” button in Power BI. However, as the documentation notes, there are some limits on the amount of data that can be exported:

  • The maximum number of rows that can be exported from Power BI Desktop and Power BI service to .csv is 30,000
  • The maximum number of rows that can be exported to .xlsx is 150,000

What’s more, clicking a button to export data and then copying it into an Excel report is a time-consuming, error-prone, manual process that no-one likes doing.

There is another way to get data from Power BI into Excel though: using the Analyze in Excel feature. Rather than using Analyze in Excel to create a PivotTable, which may suffer from the subtotals issue described here if you aren’t using the click-to-run version of Excel 2016 and as a result may be very slow when dealing with large amounts of data, and which will be awkward to get data out of because you have to use Excel functions like GetPivotData(), in this post I’ll show you how to get data from Power BI into an Excel table instead.

First of all you need to create a PivotTable in Excel on your desktop that is linked to a dataset published to Power BI. You can do this either by clicking the Analyze in Excel option from inside the Power BI service in the browser (see here for how to do this), or by using the Connect to Data option in the Power BI Publisher for Excel add-in.

Next, drag any measure into your PivotTable (you will need to have at least one measure defined in your dataset to do this) like so:

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Then double-click inside a cell containing values, such as the selected cell in the screenshot above, or right-click on the cell and select Show Details:

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When you do this a new worksheet will appear with a table in it containing rows of data from a table in the underlying dataset, but the exact data is irrelevant here. The real point is that you now have an Excel table (not a PivotTable) with a connection back to your Power BI dataset and you can edit the query that it uses to return data from Power BI – a variation on an old trick known to SSAS and Power Pivot users. You can now delete the PivotTable you created because you will no longer need it.

On the new worksheet with the table on it, right-click in a cell and select Table then Edit Query:

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A dialog will pop up, and you’ll see an MDX Drillthrough statement in the Command Text box as shown below:

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You can replace this statement with any MDX or DAX query you want – I recommend using DAX queries here because they are likely to be easier to write if you already know how to write DAX calculations, and unlike MDX queries they return a tabular resultset. I have a fairly old series of posts on DAX queries here that will help get you going. It will be a good idea to install DAX Studio and write your queries there, then copy them into Excel when you are happy with them.

Once you have a working DAX query in the Command Text box:

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You can click OK, the query will run and you’ll see the output of the query in the Excel table:

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One minor annoyance is that the column names will be in DAX ‘Table Name’[Column Name] format, and although you can use the SELECTCOLUMNS() DAX function to alias your column names and thereby remove the table names, the square brackets around the column names will always be there.

There are several good things about this approach to getting data into Excel:

  • It allows you to exceed the 150,000 row limit of the native Power BI Export option mentioned above
  • The queries are very quick to run if you aren’t doing anything complex in them
  • It avoids manual exporting – you just use Excel’s native Refresh functionality to run the query whenever you want to download new data into Excel

There are some obvious downsides though:

  • There’s no easy way to pass parameters to the queries you use, and so allow the user to choose what data is retrieved from Power BI. I guess it would be possible with some VBA, though – I haven’t tried – and it may also be possible to connect Power Query/Get&Transform to the Power BI Service and then use some of the tricks I show in this video for building reporting solutions in Excel. You can of course use Excel’s own native table filtering functionality to filter the data that is downloaded.
  • If your DAX query is slow to run your users may get frustrated. To counter this you could create calculated tables in your Power BI dataset using the same DAX as your query, and because calculated tables are created when the Power BI dataset is refreshed rather than when your user refreshes their Excel worksheet this should speed things up. However it will increase the size of your Power BI dataset and make your dataset refresh take longer. In Excel your DAX query would simply be something like:
    EVALUATE ‘My Calculated Table Name’
  • Writing DAX can be complex, whether it’s a DAX query or a calculated table, so another option would be to use the Power BI Query Editor to create the table you need for your report, load that into your dataset and then load the table into Excel.
  • You can’t publish the Excel workbook up to Power BI and have it refresh automatically, because of course Power BI does not support connections from published Excel workbooks back to Power BI datasets. Hopefully this will change in the future – it marked as planned on the Ideas forum.

Of course doing this goes against the best practices that I and most other people recommend for Power BI, so you should probably only do this if you have no other choice. Sometimes you have to bend the rules a little to make sure your project succeeds…

Upcoming Power BI and Azure SSAS training in the UK, Israel and the Netherlands

If you have some training budget to spare why not come along to one of the pre-conference seminars/training courses I have coming up in the next few months? Specifically:

  • Introduction to Azure Analysis Services – a pre-conference seminar on Thursday 22nd February at SQLBits 2018 in London. You’ll learn about what Azure Analysis Services is, why you should use it and how to build Tabular models for it. More details and registration here.
  • Power BI for analysts and developers – a three-day course covering the whole Power BI development lifecycle in Herzliya, Israel, on March 12th-14th. Full agenda and registration here.
  • Loading and transforming data in Power BI and Power Query – a pre-conference seminar on Friday 23rd March before the Dutch Power BI User Day in Utrecht. It will cover everything you need to know about the Query Editor in Power BI and Excel, going from the basics to more advanced topics such as parameters, functions and the M language. Full agenda here.

Incidentally, if you’re in London for SQLBits don’t forget to come to the London Power BI User Group meeting on Wednesday 21st February: I’m doing a panel discussion with various other Power BI folks. I’m also going to be speaking at the Dublin Data and BI Summit (run by the Power BI User Group) at the end of April, and at several other user groups later in the year; follow me on Twitter (I’m now @cwebb_bi) to find out the details when they’re available. I hope to see you at one of these events!

Using SSAS Multidimensional As A Data Source For Power BI (Video)

The nice people at PASS have made a video of my session on “Using SSAS MD as a data source for Power BI” available to view for free on YouTube:

I’m honoured that it’s listed one of their “Best of PASS Summit 2017” sessions, and there are lots of other great videos on the same page including Alberto Ferrari’s session on DAX optimisation.

Some of the tips in this video include a few things I’ve been meaning to blog about for a while, including how important it is to set the ValueColumn property on your dimension attributes in SSAS MD – it lets you use lots of functionality in Power BI that isn’t otherwise available, including date slicers.

Setting SQL Server Connection String Properties In Power BI and SSAS Tabular Modern Data Sources

It may not be immediately obvious, but you cannot set your own connection string properties when connecting to SQL Server using the built-in SQL Server connector from either Power BI or a modern data source in Azure SSAS/SSAS Tabular 2017:

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All you can do is configure the options that are available in the UI, which in the current version of SSDT looks like this:

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…and which are documented in the Sql.Databases() M function here.

It turns out that the restriction on using your own connection string properties in the built-in SQL Server connector is a deliberate design decision on the part of the Power Query team because, behind the scenes, they use different providers in different circumstances to optimise performance, and because allowing arbitrary connection string properties might make maintaining backwards compatibility difficult in the future.

While your average Power BI user is unlikely to even notice this, for SSAS Tabular developers it could be a big problem: complete control over the connection string is often necessary in enterprise BI scenarios. What are the alternatives then? Well you can use the OLE DB and ODBC connectors instead:

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Both of these connectors do allow you to set your own connection string properties. For example here’s the UI for a new ODBC connection in SSDT:

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The documentation for the Odbc.DataSource and OleDb.DataSource M functions has more detail on how these connectors can be used and how connection string properties can be set. Remember also that the OLE DB Provider for SQL Server was un-deprecated in October 2017.

However, apart from possible performance differences between the two (which you should test yourself – Henk van der Valk wrote a good post on this for SSAS MD and most of what he said is relevant for Tabular) there’s one less-than-obvious difference between these two options: the OLE DB connector does not appear to support query folding right now whereas the ODBC connector does. Of course this isn’t an issue if you’re writing your own SQL queries to import data, but if you do want to use M functions for partitioning (as I show here) you’re likely to get very poor performance with the OLE DB connector.

Using Your Own SQL Queries For Tables With Modern Data Sources In SSAS 2016+ And Azure Analysis Services

While the integration of the Power Query engine into Analysis Services Tabular 2017 and Azure Analysis Services with modern data sources will certainly bring a lot of benefits, I think it’s fair to say that the implementation has not been entirely painless. One problem is that it is no longer obvious how to specify your own SQL query to populate a table or partition in your Tabular model – and while the Query Editor is great, there are a lot of cases where this is necessary. In this post I’ll show you how to do this.

If you’re used to using the Power Query UI in Excel or Power BI Desktop, you’ll notice that when you connect to a SQL Server database using the SQL Server connector in SSDT:

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…there is no option to enter your own SQL query when you do so:

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This is deliberate. In Analysis Services, unlike Power BI and Excel, there is a distinction made between data sources and other M queries that return data from those data sources, one that makes a lot of sense in my opinion. While it is possible to enter your own SQL for other data source types, such as OLE DB connections, a data source object is really intended just to define a connection to a data source and not to define what data you want from that data source.

[You may also notice that there’s a “SQL statement” property on a SQL Server data source visible in the Visual Studio properties pane, but I don’t recommend you use it – it doesn’t seem to work well with the rest of the SSDT/Power Query UI]

To import a table or view in your database all you have to do is right-click on your data source and choose Import New Tables; my blog post from September last year describes how to do this, and how to use M functions for creating partitions.

To use your own SQL queries though you need to write some M code. First, import a table – any table, but preferably a small one – and get to the Query Editor UI. In this case I’ve imported the DimDate table from the Adventure Works DW database:

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Next, select your query in the Queries pane on the left-hand side of the screen and open the Advanced Editor either by clicking on the relevant button in the toolbar (shown above) or by right-clicking on the query name in the Queries pane. You’ll see the following dialog:

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The M code will be something like this:

let
    Source = #"SQL/localhost;Adventure Works DW",
    dbo_DimDate = Source{[Schema="dbo",Item="DimDate"]}[Data]
in
    dbo_DimDate

In this example the Source step creates a reference to the data source you have already created, and the dbo_DimDate step gets the contents of the DimDate table from this data source.

You can modify this code to use your own SQL by using the Value.NativeQuery() function (which I have blogged about here):

let
    Source = #"SQL/localhost;Adventure Works DW",
    MyQuery = 
	Value.NativeQuery(
		#"SQL/localhost;Adventure Works DW",
		"SELECT DISTINCT FiscalYear FROM DimDate"
	)
in
    MyQuery

Here what I’ve done is replaced the dbo_DimDate step in the previous query with a step called MyQuery that uses Value.NativeQuery() to run my own SQL.

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Now all you need to do is click Import and you have the output of the query loaded into SSAS. It would be nice if there was UI support for using your own SQL queries when importing data in the future. Note that, as soon as you use this method, any other steps or queries further downstream will not be able to perform query folding, so you should make sure that you do as much of your filtering and transformation in the SQL as possible otherwise you may encounter performance problems.

The documentation describes a similar – but not identical – workflow for achieving the same result here. Personally I think it’s counter-intuitive that you should click on Expressions to create a Table object! Expressions are used for functions and other M code that is shared by the M queries used by Tables.

An alternative to doing all this is to go back to the old way of doing things and use a legacy data source rather a modern data source in SSDT. You lose the ability to use the Query Editor and M if you do this, but in a lot of cases you probably won’t care. The 17.4 release of SSDT for Visual Studio 2015, released in December 2017, has exposed a property that allows you to create legacy data sources again easily. In Visual Studio, go to the Tools menu and select Options and in the Options dialog go Analysis Services Tabular/Data Import and check “Enable legacy data sources”:

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When you do this, you’ll notice two new options when you right-click on Data Sources in the Tabular Model Explorer pane: Import From Data Source (Legacy) and Existing Connections (Legacy).

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This gives you access to the Table Import wizard that was available in previous versions of Analysis Services Tabular, which not only allows you to enter your own SQL but also creates a legacy data source that in turn makes it easy to use your own SQL when creating partitions.