Ensuring Columns Are Always Present In A Table Returned By Power Query

Disappearing or renamed columns in your data source can cause all kinds of problems when you’re importing data using Power Query: errors when you try to refresh the query, broken calculations in Power Pivot, PivotTables that reformat themselves and then need to be manually recreated. As a result, it can be a very good idea to build some logic into your Power Query queries that ensures that a table always contains the columns you’re expecting.

Consider the following csv file:

image

In Power Query, if you connect to it and create a query you’ll end up with something like this:

let
    Source = Csv.Document(File.Contents("C:\Demo.csv"),null,",",null,1252),
    #"First Row as Header" = Table.PromoteHeaders(Source),
    #"Changed Type" = Table.TransformColumnTypes(#"First Row as Header",{{"Sales", Int64.Type}})
in
    #"Changed Type"

Let’s assume that this query is called GetSourceData. Let’s also assume that your output from Power Query should always be a table that has the three columns Product, Month and Sales, and that Product and Month should be text columns and Sales should be numeric. The basic steps to take to ensure that this always happens, even if the columns in the csv file change, are as follows:

  1. Create a query that connects to your data source, for example like GetSourceData above
  2. Create a query that will always return a table with the columns you want, but which contains no rows
  3. Append the second table onto the end of the first table. This will result in a table that contains all of the columns from both tables.
  4. Remove any unwanted columns.

There are a number of ways to create the empty table needed in step 2. You could use the #table() function if you’re confident writing M code, and the following single line query (no Let needed) does the job:

#table(
 type table [Product=text, Month=text, Sales=number],
 {})

image

Alternatively, if you wanted something that an end user could configure themselves, you could start with a table in Excel like this:

image

then transpose it, use the first row of the resulting table as the header row, then set the data types on each table to get the same output:

let
    Source = Excel.CurrentWorkbook(){[Name="Columns"]}[Content],
    #"Transposed Table" = Table.Transpose(Source),
    #"First Row as Header" = Table.PromoteHeaders(#"Transposed Table"),
    #"Changed Type" = Table.TransformColumnTypes(#"First Row as Header",
	{{"Product", type text}, {"Month", type text}, {"Sales", Int64.Type}})
in
    #"Changed Type"

Assuming that this query is called ExpectedColumns, it’s then a trivial task to create a third query that appends the ExpectedColumns query onto the end of the GetSourceData query. If GetSourceData includes all the columns it should then this append will have no effect at all; if some of the columns have changed names or disappeared, you’ll see all of the columns present from both GetSourceData and ExpectedColumns in the output of the append. For example if the Month column in GetSourceData is renamed Months then the output of the append will look like this:

image 

Finally, in this third query you need to select all the columns you want (ie all those in the ExpectedColumns query) and right click/Remove Other Columns, so you remove all the columns you don’t want. In the previous example that gives you:

image

The point here is that even though the Month column only contains nulls, and the actual month names have been lost, the fact that the columns are all correct means that you won’t get any errors downstream and your PivotTables won’t be reformatted etc. Once you’ve fixed the problem in the source data and refreshed your queries, everything will go back to normal.

Here’s the code for this third query:

let
    Source = GetSourceData,
    Append = Table.Combine({Source,ExpectedColumns}),
    #"Removed Other Columns" = Table.SelectColumns(Append,{"Product", "Month", "Sales"})
in
    #"Removed Other Columns"

For bonus points, here’s another query that compares the columns in GetSourceData and ExpectedColumns and lists any columns that have been added to or are missing from GetSourceData:

let
    //Connect to Excel table containing expected column names
    ExcelSource = Excel.CurrentWorkbook(){[Name="Columns"]}[Content],
    //Get list of expected columns
    ExpectedColumns = Table.Column(ExcelSource, "ColumnName"),
    //Get a list of column names in csv
    CSVColumns = Table.ColumnNames(GetSourceData),
    //Find missing columns
    MissingColumns = List.Difference(ExpectedColumns, CSVColumns),
    //Find added columns
    AddedColumns = List.Difference(CSVColumns, ExpectedColumns),
    //Report what has changed
    OutputMissing = if List.Count(MissingColumns)=0 then
                     "No columns missing" else
                     "Missing columns: " & Text.Combine(MissingColumns, ","),
    OutputAdded = if List.Count(AddedColumns)=0 then
                     "No columns added" else
                     "Added columns: " & Text.Combine(AddedColumns, ","),
    Output = OutputMissing & "   " & OutputAdded
in
    Output

image

You can download the sample workbook for this post here.

Automatically Generating Date Dimension Tables In Excel 2016 Power Pivot

As you probably know, whenever you are doing any kind of date or time-based calculations in DAX you should always have a separate Date table in your Power Pivot model. There are a number of ways of building these tables (see, for example, my Power Query query here) but they are all a bit of a hassle – which is why it’s so cool that, in Excel 2016, you can get one built automatically inside the Power Pivot window.

Consider the following table of sales data on an Excel worksheet:

Source

With this table loaded into the Data Model (and the Order Date column recognised as containing data of the Date data type), when you go to the Design tab in the Power Pivot window you’ll see the new Date Table button enabled:

Menu

Clicking on the New button will add a new date table to the Data Model, called Calendar:

CalendarBasic

This table is automatically marked as the Date Table in your model.

The table contains a continuous range of dates starting from the beginning of the year of the earliest date found in any column in any table in your Data Model, up to the end of the year containing the latest date found in any column in any table in your Data Model. Obviously, this means that your table could contain a very large date range if, for example, you have a Customer table containing a Date Of Birth column. Luckily, you also have the option of manually configuring the range of dates used by clicking the Update Range button:

Range

One other thing to point out is that the resulting table is a table like any other, so you can add, delete or rename columns as you wish. You should also be able to set the table back to its default state by using the Set Default menu option, but I couldn’t make that work (possibly it hasn’t been implemented yet – this post was written using the Excel 2016 Preview).

If you do make changes like adding calculated columns, such as the Month Year calculated column shown below:

Calc

You can then click the Save Configuration button to save the current state of the table as your default. This means that the next time you create a new Date table in the same workbook, the table will include any customisations. However these changes don’t seem to be applied in Date tables created in new workbooks – maybe this will also change before RTM?

All in all, this is a very handy feature that will save Power Pivot modellers a lot of time. I wonder if it uses the new Calendar() or CalendarAuto() DAX functions under the covers?

Power Query/Excel 2016 VBA Examples

In Excel 2016, Power Query is no longer an Excel add-in but a native feature of Excel, and what’s more, you can now use VBA to create and manage Power Query queries.

I’ve found two sources of information about how to use VBA with Power Query in Excel 2016. First, there are some code samples on the Technet Gallery here:
https://gallery.technet.microsoft.com/VBA-to-automate-Power-956a52d1#content
…and Gil Raviv, a Program Manager at Microsoft, has also asked for feedback on this functionality on this thread:
https://social.technet.microsoft.com/Forums/en-US/1eac9c36-b6e4-48f0-a51a-fa92b24cf1d9/vba-and-power-query-in-excel-2016-preview-lets-get-started?forum=powerquery

Secondly, I was contacted recently by Tycho Grouwstra who shared with me some of the interesting work he has done using VBA and Power Query in the Excel 2016 Preview, and who has very kindly allowed me to blog about it here. His work is much more representative of how I think most people will want to use this feature.

Tycho sent me a .xlsm file containing all of the VBA code, which you can download here. Obviously the code only works in the Excel 2016 Preview, but you can still open the file and look at the code in Excel 2013. However if you’re worried about downloading a workbook with macros in, I extracted the code to a text document which you can see here. If you want to copy the code to use in your own workbook, you’ll need to go to the VBA Editor, select Tools/References and add a reference to “Microsoft ActiveX Data Objects 6.1 Library”.

image

The VBA code includes examples of how to:

  • Delete all the Power Query queries in a workbook
  • Export/import the M code for all queries to/from another Excel workbook
  • Export/import the M code for all queries to text files
  • Refresh all the Power Query queries in the workbook
  • Load a query to an Excel table

A few bugs/features in the Preview are also pointed out, namely:

  • Imported queries don’t always show up in the Workbook Queries pane; the workaround is to close and reopen the workbook
  • Functions aren’t recognised as functions (ie they don’t have the fx icon) until you open the Query Editor and the Close & Load
  • Query groups aren’t supported yet – which is a bit of an oversight, in my opinion, but the forums thread linked to above indicates it won’t be addressed before RTM unfortunately
  • Loading the output of a query into an Excel table using the code given here doesn’t seem to have the same result as loading a query to a table in the worksheet using the Power Query UI: it creates a blue, rather than green, table that doesn’t always retain row order.

I can imagine a lot of serious Power Query users will create workbooks containing a library of their most useful queries and functions, and use VBA code to copy these queries and functions into new workbooks as and when necessary. We’ll have to wait and see what Microsoft’s plans for sharing Power Query queries are, whether they’ll go beyond what’s already been seen in Office 365 Power BI, whether they will be part of a bigger bundle of services and what the cost will be.

Incidentally, the sample workbook contains a lot of interesting, generally useful Power Query queries and functions written by Tycho and others which is also available in the following GitHub repository: https://github.com/tycho01/pquery

Using SelectColumns() To Alias Columns In DAX

A few years ago I wrote this post on how to alias columns in a table in DAX, using a combination of AddColumns() and Summarize(). The good news is that in Excel 2016/the Power BI Designer/SSAS Tabular 2016 there’s a new DAX function specifically for this purpose: SelectColumns(). Here’s an example of how it can be used:

Imagine you have the following source table, called Products:

image

You can write a DAX query to get all the rows and columns from this table like so:

EVALUATE Products

Here’s the output of that query in DAX Studio (and remember, DAX Studio can connect to data loaded into the Power BI Designer, which is what I’m doing here):

image

You can alias the columns in this table using SelectColumns() very easily, like so:

EVALUATE
SELECTCOLUMNS (
    Products,
    "Column One", Products[Product],
    "Column Two", Products[Colour]
)

Here’s the output:

image

The syntax for SelectColumns() is straightforward: the first parameter is a table expression, and after that there are pairs of parameters consisting of:

  • A new column name
  • An expression returning a column from the table given in the first parameter

As you can see in the output of the query above, I’ve renamed the Product column “Column One” and the Colour column “Column Two”.

This means I can now crossjoin a table with itself without needing to worry about conflicting column names, like so:

EVALUATE
CROSSJOIN (
    Products,
    SELECTCOLUMNS (
        Products,
        "Column One", Products[Product],
        "Column Two", Products[Colour]
    )
)

image

One other interesting thing to note about SelectColumns() is that it allows you to do projection in a DAX query easily – as Marco notes here, it was possible before but it wasn’t pleasant. For example, the query:

EVALUATE
SELECTCOLUMNS (
    Products,
    "Just Colour", Products[Colour]
)

Returns:

image

Notice how there are three rows in the output here and that the value Green occurs twice. If you’re a true DAX afficionado, you might get excited about that.

Thoughts On All The Recent Power BI/SQL Server 2016 BI/Excel 2016 News

The last few weeks have seen more Microsoft BI-related announcements in a short time than I can ever remember before. Some of them I’ve blogged about; most I’ve at least tweeted. For good summaries of what’s coming for Power BI, on-premises SQL Server BI and Excel 2016 I can recommend the following posts by other people, all of which are worth reading:

http://www.jenunderwood.com/2015/05/14/sql-server-bi-2016/

http://www.jenunderwood.com/2015/04/23/april-microsoft-bi-world-news/

http://byobi.com/blog/2015/05/ssas-related-enhancements-in-sql-server-2016/

https://gqbi.wordpress.com/2015/05/14/bi-nsight-excel-2016-power-bi-updates-including-new-data-sources-azure-sql-data-warehouse/

https://gqbi.wordpress.com/2015/05/07/bi-nsight-sql-server-2016-power-bi-updates-microsoft-azure-stack/

Even then I’m not sure everything has been covered, and because new stuff is coming thick and fast (custom regions in Power Map! DirectQuery/ROLAP in the cloud with Power BI connecting to Azure SQL Database!) it’s hardly worth trying. However, I do think this is as good a point as any to work out what I think about all this activity and where Microsoft is heading.

SSAS Multidimensional Improvements

I’m well past the stage of feeling angry about the neglect of SSAS Multidimensional over the past few years, and I’m genuinely grateful that it’s getting some investment rather than nothing at all. That said, I’m not sure which customers asked for Netezza support or DBCC – they aren’t things I’ve ever needed. The promised performance improvements are where I expect the real value to be, and on their own they will probably give existing customers reason enough to upgrade to 2016. It would have been nice to get even one new feature from this list though.

SSAS Tabular Improvements

As expected, the Tabular engine in SSAS 2016 gets a lot of new stuff for free because of its shared heritage with other Power BI tools. My feeling is that uptake of Tabular has been slower than it should have been because 2012 was, frankly, a bit v1.0 with all the immaturity that implies, and there haven’t been any substantial improvements since then. With 2016, though, it looks like Tabular will take a great leap forward and as a result be seen as a much more capable platform. There will certainly be fewer reasons to choose Multidimensional over Tabular, although for applications that require complex calculations (such as financial applications) Multidimensional will still have the upper hand. The more reasons I have to love Tabular, the less I’ll worry about the lack of new features in Multidimensional.

Power Query And The Corporate/Self-Service BI Crossover

As regular readers of this blog may have noticed, I like Power Query a lot and I’m pleased to see that it has extended its reach into corporate BI. Power Query as a data source for SSAS will be important for scenarios where Power Pivot models are upgraded to server-side solutions; I don’t think it will be a good idea to use Power Query if you’re building an SSAS solution from scratch though. Power Query in SSIS was another predictable development and one which should make it easier to work with certain data sources (such as Excel files); the existing ability to publish the output of an SSIS package as an OData feed using the Data Streaming Destination, which can then be consumed by Power Query, could open up some interesting scenarios where a user builds a data set in Power Query and publishes it via SSIS for consumption by other Power Query users.

It’s the promised integration of Power Query and SSRS that excites me most though. I asked for it here and it looks like my wish has been granted! As well as providing access to a wider range of data sources and a common ‘get data’ experience with other tools, I think it will be the key to making SSRS and in particular Report Builder the self-service BI tool that so many customers want it to be. Report Builder has struggled with two problems since it first appeared: first, make it easier for users to lay out a nice-looking report on a canvas, something that the current version does a reasonable job of I think; and second, make it easy for non-technical users (who, for example, might have little or no SQL knowledge) to get data from data sources for their reports – this is where it has not succeeded in the past, and where Power Query could make all the difference. Power Query, among other things, is a solid, user friendly, SQL generation tool. This, plus the fact that SSRS will be updated for all modern browsers and get new visualisations and report themes etc, means that the vast number of existing SSRS customers will have a lot of good reasons to upgrade to 2016, and when they do they’ll also find it easy to integrate with the rest of Power BI.

Power BI: Will Anyone Buy It?

It’s very easy for Microsoft BI fanboys like me to get all worked up by the constant drip feed of tweets about new Power BI features. An impartial observer will point out that some of these features, like the ability to change the colours of your charts in Power View, are actually things we should be embarrassed at not having already. Nonetheless I think it’s fair to say that Microsoft are doing a good job of getting its core customers excited about Power BI and there’s also a lot of evidence that people outside this core at, at least, curious, so from a marketing perspective everything’s going well.

Even if the marketing is good, that will only get Power BI evaluated. Those evaluations will only turn into purchases if the product itself is up to the task. Microsoft set itself an extremely difficult task when it decided to change the direction of Power BI and deliver a respectable version 1.0 this year; the impressive speed that new features are arriving at suggests that they will manage it. When this product is put side-by-side with competing tools it will have some advantages – Power Query is excellent, the Power Pivot engine is fast and can handle all kinds of complex calculations – but will inevitably appear immature in other respects such as visualisation. I think the limit on the amount of data that can be held in a single data model, either on the desktop or in the cloud, is also something that will be a problem for those of us who are used to building server-side SSAS solutions that can hold all the data the user ever needs to see. Maybe DirectQuery/ROLAP on SQL Azure and perhaps Azure SQL Data Warehouse will make this irrelevant? Overall though in my opinion the version of ‘new’ Power BI that will RTM later this year will be seen as more than good enough from a technical standpoint, and if this rate of change is maintained for version 2.0 then it will be something special.

I also think that the focus on building APIs and connectors to other web services is a really clever move. There are a lot of other vendors out there who don’t want to build their own BI functionality, and if Microsoft can convince them to use Power BI that will bring a lot of customers on board. Even at this early stage it looks like Microsoft is doing a good job of recruiting these vendors (SQL Sentry for example, but there are many others) as well as getting other teams inside Microsoft (like Visual Studio Online) to do the same. Close integration with new Microsoft services like Azure Stream Analytics and Azure SQL Data Warehouse should have a similar effect, although less pronounced given that these new services will have few users initially.

While I admit the divorce from Excel was the right thing to do in the circumstances, I still find that I prefer working in Excel over the Power BI Dashboard Designer. Maybe that’s partly due to habit, but Power View still has a long way to go before it has the flexibility of Excel PivotTables and especially cube formulas. That’s why I think Marco Russo’s campaign to create an API for the Dashboard Designer and to support external connections from Excel and other tools is so important. If you haven’t voted already, please do so now! This would be a killer feature in that it would allow you to continue to build reports in Excel (maybe 32-bit) while still making use of new features in the engine. It would give use all the good things we have today with the Excel Power add-ins and more. It would also, as Marco points out, be another reason for third party vendors to use the Power BI platform.

The final factor to consider is price. Making the Dashboard Designer free is important, because it’s not just a Dashboard Designer but a complete, standalone desktop self-service BI solution in itself. Many customers will use it as such without buying a Power BI subscription – that is, if they know that is an option. The free/$9.99 cloud subscription model is also very attractive, and all in all the new pricing model is a refreshing change from the nightmare that ‘old’ Power BI licensing was. I wonder if there will be any particular incentives (financial or otherwise) for partners to sell or recommend Power BI to their customers? If not,there probably should be.

Conclusion

Overall, I’m happier with the direction that Microsoft BI is going in than I have been for a long time. Power BI now seems like it has some momentum behind it, and that it is a coherent product rather than a collection of (individually impressive) tools bound into Excel that, for one reason or another, customers couldn’t use to their full potential. We’ll have to see whether it does become a commercial success or not but I think it has a good chance of doing so now. Excel 2016 also has some welcome improvements, even if it is now the ‘slow track’ for self-service BI; the more users discover Power Pivot and Power Query via Excel 2013 and soon 2016, the more likely it is that they’ll start using the rest of the Power BI stack.

Meanwhile it seems like at last there is at last a serious commitment to improve the on-premises SQL Server BI stack on the part of Microsoft. Some time ago I wrote a post on why corporate BI and self-service BI are both necessary and I still stand by what I said there; it’s also clear that a lot of customers, especially enterprise customers and especially in Europe, are not yet ready to put their most valuable data in the cloud. Microsoft has the chance to be one of the few vendors with great self-service and corporate BI stories, and great on-premises and cloud BI stories. Also, given that today’s SQL Server BI customers are the most likely to become tomorrow’s Power BI customers, keeping them happy in the medium term while Power BI matures should be a priority.

Let’s see where we are this time next year…?

Power Query Announcements At The PASS BA Conference

There were a couple of big (well, big if you’re a Power Query fan like me) announcements made today by Miguel Llopis at the PASS BA Conference:

  • Today Power Query is available only to people who have Excel Professional Plus or Excel standalone, but as of May a version of Power Query will be available on every Excel SKU. There will be some limitations around data sources that are supported if you don’t have Excel Professional Plus, but that’s ok – this change will make it much easier for people to learn about and use Power Query, and I’m really happy about that.
  • Other new features coming in the May update of Power Query include the ability to turn off prompts about native database queries (useful in this scenario, for example), OData v4.0 support, the ability to use alternative Windows credentials to run queries, and a couple of new transformations such as removing empty rows.
  • Excel 2016 – where Power Query is now native to Excel – will have support for creating Power Query queries using VBA and macro recording. I understand you won’t be able to edit individual steps in a query, but you’ll be able to create and delete queries programmatically and change where they load their data too.
  • Excel 2016 will also support undo/redo for Power Query and give you the ability to copy/paste queries (even from workbook to workbook).
  • There was a commitment that Power Query in Excel 2016 will keep getting updates on a regular basis, rather than get tied to the much slower Office release cycle, so it retains parity with the Power Query functionality in the Power BI Dashboard Designer.

All very cool stuff!

Documentation For New Excel 2016 DAX Functions

Microsoft has published documentation for the new DAX functions in the Excel 2016 preview here:

https://support.office.com/en-us/article/New-DAX-functions-for-Excel-2016-Preview-8192a787-aa91-4d7f-9a82-4e2c607e629a

There’s a lot of detail, including examples (although the ConcatenateX() page isn’t live at the time of writing – but I’ve blogged about that already), so it’s well worth reading through.