Drillthrough On Calculated Members In SSAS MD 2017 Using DAX Expressions, Part 2

If you read part 1 of this series you probably already have a good idea of how I’m going to use DAX queries in actions to implement drillthrough on calculated members. However, there is one last major problem to solve – and no 100% fool-proof way of solving it.

That problem is that there is a maximum length of (as far as I can tell) 32768 characters for the DAX query that is generated by the action. If you exceed that limit you’ll see an error in Excel when you drillthrough:

image

This is the result of the generated DAX query being truncated before Excel tries to run it. As you can imagine, if you have large dimensions and you’re generating a DAX query with thousands of key values in an IN expression, it’s very easy to hit the maximum query length. What can you do to make this less likely?

Probably the most effective method is to check whether the IN clause will contain all of the possible key values on the dimension (most likely because no attributes from the dimension are used in the query), and if so don’t bother including that dimension in the DAX query. Here’s an example of how this can be done:

IIF(
COUNT(EXISTING [Date].[Date].[Date].MEMBERS) = 
COUNT([Date].[Date].[Date].MEMBERS),
"",
",'Date'[Date.Key0] IN {
" +
GENERATE(EXISTING [Date].[Date].[Date].MEMBERS , 
[Date].[Date].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "}
")

Another option is to use NonEmpty() to remove any members from the drillthrough that have no data, like so:

IIF(
COUNT(EXISTING [Date].[Date].[Date].MEMBERS) = 
COUNT([Date].[Date].[Date].MEMBERS),
"",
",'Date'[Date.Key0] IN {
" +
GENERATE(EXISTING 
NONEMPTY([Date].[Date].[Date].MEMBERS, [Measures].[Sales Amount]) 
, [Date].[Date].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "}
")

However, if these techniques (and there may be others) still don’t reduce the length of the query to an acceptable length you will want to try to fail as gracefully as possible and show a more helpful error message than the one above. You can do this with the DAX Error() function, like so:

IIF(
COUNT(EXISTING [Customer].[Customer].[Customer].MEMBERS) = 
COUNT([Customer].[Customer].[Customer].MEMBERS),
"",
",'Customer'[Customer.Key0] IN {
" +
IIF(COUNT(
{EXISTING 
NONEMPTY(
[Customer].[Customer].[Customer].MEMBERS, 
[Measures].[Sales Amount])} 
AS CustomerList)>7000,
"ERROR(
""Please reduce your selection on the Customer dimension
 or remove it from your PivotTable"")",
GENERATE(
CustomerList
, [Customer].[Customer].CURRENTMEMBER.PROPERTIES("KEY"), ",")
)
+ "}
")

In this example, if the resulting DAX IN expression for the Customer dimension will have more than 7000 keys in it, the entire DAX query returns a custom error message instead:

image

Once again this is a far from perfect solution – I would have liked to test the total number of characters in the query, but if you do that you have to write the expression twice, once in the first parameter of IIF() and once in one of the results, and that would be horrible. My gut feeling is that you should only use this technique on dimensions with a large number of members on the key attribute.

Putting this all together, for a simple cube based on data from Adventure Works with three dimensions (Date, Product and Customer) here’s what a complete Action Expression for a regular measure might look like:

"EVALUATE 
FILTER(
CALCULATETABLE(
SELECTCOLUMNS(
'Sales Order', 
""Sales Order Number"",
'Sales Order'[Sales Order Number],
""Sales Order Line Number"",
'Sales Order'[Sales Order Line Number],
""Sales Amount"",
[Sales Amount])
" +
IIF(
COUNT(EXISTING [Date].[Date].[Date].MEMBERS) = 
COUNT([Date].[Date].[Date].MEMBERS),
"",
",'Date'[Date.Key0] IN {
" +
GENERATE(EXISTING 
NONEMPTY([Date].[Date].[Date].MEMBERS, 
[Measures].[Sales Amount]) 
, [Date].[Date].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "}
") +
IIF(
COUNT(EXISTING [Customer].[Customer].[Customer].MEMBERS) = 
COUNT([Customer].[Customer].[Customer].MEMBERS),
"",
",'Customer'[Customer.Key0] IN {
" +
IIF(
COUNT(
{EXISTING NONEMPTY([Customer].[Customer].[Customer].MEMBERS, 
[Measures].[Sales Amount])} AS CustomerList)>7000,
"ERROR(""Please reduce your selection on the Customer dimension 
or remove it from your PivotTable"")",
GENERATE(
CustomerList
, [Customer].[Customer].CURRENTMEMBER.PROPERTIES("KEY"), ",")
)
+ "}
") +
IIF(
COUNT(EXISTING [Product].[Product].[Product].MEMBERS) = 
COUNT([Product].[Product].[Product].MEMBERS),
"",
",'Product'[Product.Key0] IN {
" +
GENERATE(EXISTING 
NONEMPTY([Product].[Product].[Product].MEMBERS, 
[Measures].[Sales Amount]) 
, [Product].[Product].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "}
") +
"),
[Sales Amount]>0)"

 

What about a calculated measure though? Assuming that  you have a time utility/date tool/shell dimension, you can use a Condition expression on the action above to make sure it only gets executed for the member on the time utility dimension that contains the non-calculated values, in this case called [Actual Value]:

([Measures].CURRENTMEMBER IS [Measures].[Sales Amount]) AND
([Date Calculations].[Date Calculations].CURRENTMEMBER IS 
[Date Calculations].[Date Calculations].&[Actual Value])

image

Now, let’s say there is a calculated member on the time utility dimension that contains a year-to-date calculation with the following definition:

CREATE MEMBER 
CURRENTCUBE.[Date Calculations].[Date Calculations].[Year-To-Date] 
AS
AGGREGATE(
PERIODSTODATE(
[Date].[Calendar].[Year],
[Date].[Calendar].CURRENTMEMBER),
[Date Calculations].[Date Calculations].&[Actual Value]);

You can create a new action that has a Condition expression as follows that restricts it to the year-to-date calculation:

([Measures].CURRENTMEMBER IS [Measures].[Sales Amount]) AND
([Date Calculations].[Date Calculations].CURRENTMEMBER IS 
[Date Calculations].[Date Calculations].[Year-To-Date])

Now, the final problem to solve is to generate a DAX query that returns all of the Sales Orders from the beginning of the current year up to and including the selected date – the Sales Orders that a user would expect to see when they drilled through on the year-to-date calculated member above.

Here’s a modified MDX expression for the Date dimension that returns a DAX expression that finds all of the dates associated with the current selection on the Date dimension, finds the maximum date, then filters the drillthrough DAX query by all dates from the beginning of the current calendar year up to and including the maximum date:

IIF(
COUNT(EXISTING [Date].[Date].[Date].MEMBERS) = 
COUNT([Date].[Date].[Date].MEMBERS),
"",
", VAR FilteredDates = FILTER('Date', 'Date'[Date.Key0] IN {
" +
GENERATE(
EXISTING 
NONEMPTY([Date].[Date].[Date].MEMBERS,[Measures].[Sales Amount]) , 
[Date].[Date].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "})
VAR MaxDate = MAXX(FilteredDates, 'Date'[Date.Key0])
VAR MaxYear = MAXX(FilteredDates, 'Date'[Year])
RETURN 
FILTER('Date', 'Date'[Date.Key0]<=MaxDate && 'Date'[Year]=MaxYear)
")

Here’s the complete MDX expression for the year-to-date drillthrough:

"EVALUATE 
FILTER(
CALCULATETABLE(
SELECTCOLUMNS(
'Sales Order', 
""Sales Order Number"",
'Sales Order'[Sales Order Number],
""Sales Order Line Number"",
'Sales Order'[Sales Order Line Number],
""Sales Amount"",
[Sales Amount])
" +
IIF(
COUNT(EXISTING [Date].[Date].[Date].MEMBERS) = 
COUNT([Date].[Date].[Date].MEMBERS),
"",
", VAR FilteredDates = FILTER('Date', 'Date'[Date.Key0] IN {
" +
GENERATE(
EXISTING 
NONEMPTY([Date].[Date].[Date].MEMBERS,[Measures].[Sales Amount]) , 
[Date].[Date].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "})
VAR MaxDate = MAXX(FilteredDates, 'Date'[Date.Key0])
VAR MaxYear = MAXX(FilteredDates, 'Date'[Year])
RETURN 
FILTER('Date', 'Date'[Date.Key0]<=MaxDate && 'Date'[Year]=MaxYear)
") +
IIF(
COUNT(EXISTING [Customer].[Customer].[Customer].MEMBERS) = 
COUNT([Customer].[Customer].[Customer].MEMBERS),
"",
",'Customer'[Customer.Key0] IN {
" +
IIF(COUNT({
EXISTING 
NONEMPTY([Customer].[Customer].[Customer].MEMBERS, 
[Measures].[Sales Amount])} AS CustomerList)>7000,
"ERROR(""Please reduce your selection on the Customer dimension or 
remove it from your PivotTable"")",
GENERATE(
CustomerList
, [Customer].[Customer].CURRENTMEMBER.PROPERTIES("KEY"), ",")
)
+ "}
") +
IIF(
COUNT(EXISTING [Product].[Product].[Product].MEMBERS) = 
COUNT([Product].[Product].[Product].MEMBERS),
"",
",'Product'[Product.Key0] IN {
" +
GENERATE(EXISTING 
NONEMPTY([Product].[Product].[Product].MEMBERS, 
[Measures].[Sales Amount]) 
, [Product].[Product].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "}
") +
"),
[Sales Amount]>0)"

I warned you it was going to be complicated, didn’t I? You can download a SSAS MD 2017 .abf backup file containing the sample database and the two actions here.

Drillthrough On Calculated Members In SSAS MD 2017 Using DAX Expressions, Part 1

Without a doubt one of the most useful features of SSAS Tabular 2017 is the new Detail Rows Expression property. It allows you to control exactly which columns and rows appear when you do a drillthrough – something that is particular important when you’re doing a drillthrough on a calculation, and something that SSAS MD users have also wanted to have for a long time now. For example, imagine that you have an Excel PivotTable that is sliced by a single date and a calculated member that shows a year-to-date sum of sales calculation: when a user does a drillthough they would expect to see data for all the fact data that contributes to the value they have clicked on, which in this case means data for all dates from the beginning of the year up to the selected date; this is what the Detail Rows Expression property makes possible and this is exactly what a regular drillthrough in SSAS MD doesn’t do.

There have been many attempts at solving this problem in SSAS MD, from Mosha’s blog post back in 2008 to these custom functions in the Analysis Services Stored Procedure Project (for a few more weeks still on Codeplex, but when Codeplex dies available here on GitHub). None of these solutions have been perfect and all have involved a certain amount of .NET code. In this series of posts I’m going to describe a slightly different approach, and while it isn’t perfect either and is very complex (you’ll need to be good at MDX and DAX to implement it) I think it has a lot to recommend it, not least because no .NET code is required. In this first post I’m going to demonstrate some of the functionality that makes my approach possible; in part 2 I’ll put it all together into a working solution.

First thing to note: you have been able to query SSAS MD using DAX as well as MDX since SQL Server 2012 SP1 CU3. Most client tools, like Excel, generate MDX queries but Power BI for example generates DAX queries when you create a Live connection to SSAS MD. To learn more about DAX support in SSAS MD this video of a session of mine from SQLBits from a few years ago is a good place to start; it’s fairly old but most of the content is still relevant.

This in turn means that you can create a Rowset action (not a Drillthrough action) in SSAS MD that return the results of a DAX query. Here’s an example of an action that does this:

image

The Action Expression property is an MDX expression that returns the text of the query to be executed and whose results will be displayed to the user as the output of the drillthrough. In this case the MDX expression consists of one string, and that string is a DAX query that returns a list of Sales Order Numbers, Line Numbers and their associated Sales Amounts:

EVALUATE 
SELECTCOLUMNS(
'Sales Order', 
"Sales Order Number",
'Sales Order'[Sales Order Number],
"Sales Order Line Number",
'Sales Order'[Sales Order Line Number],
"Sales Amount",
[Sales Amount])

Here’s the result in Excel:

image

image

This is just a static query though, and for an action you will need to generate a query dynamically to return an appropriate table of data depending on which cell the user has drilled through on.

However before I carry on there’s an important question that needs to be addressed. You may be wondering why I’m using a DAX query for this, when I could be using an MDX DRILLTHROUGH statement (as in the approaches linked to above) or an MDX SELECT statement. The problem with a DRILLTHROUGH statement is that it can only accept an MDX SELECT statement that returns a single cell in its first parameter; this means it’s not possible to get it to return more complex resultsets like the one required for the year-to-date example above. Normal MDX SELECT statements don’t suffer from this restriction and it would indeed be possible to dynamically generate one that meets any need. Unfortunately when the results of an MDX SELECT statement are returned from a Rowset action you have no control over the format of the column headers that are returned, and they are often not pretty at all. A DAX query, in contrast, gives you complete control over the data that is returned and the way the column headers are formatted.

The last question I’m going to address in this post is how the DAX query can be made dynamic. To do this I’m going to use the new DAX IN operator, which is only available in SSAS 2017. As always with DAX, there’s a great article describing it written by Marco Russo here:

https://www.sqlbi.com/articles/the-in-operator-in-dax/

Here’s how the DAX query above can be adapted to return the Sales Orders for just two dates using the IN operator:

EVALUATE 
FILTER(
CALCULATETABLE(
SELECTCOLUMNS(
'Sales Order', 
"Sales Order Number",
'Sales Order'[Sales Order Number],
"Sales Order Line Number",
'Sales Order'[Sales Order Line Number],
"Sales Amount",
[Sales Amount]),
'Date'[Date.Key0] IN {20030101, 20030102}),
[Sales Amount]>0)

image

In this example, the ‘Date’[Date.Key0] column is the column that contains the key values of the Date attribute on the Date dimension in my SSAS cube. To make this dynamic, you need an MDX expression that will return a query like the one above and, in particular, return a different list of date keys depending on what the user has drilled through on. The MDX GENERATE() function can be used to do this: you can use it to iterate over the set of existing members on the Date attribute of the Date dimension and output a comma-delimited list of key values from each member:

"EVALUATE 
FILTER(
CALCULATETABLE(
SELECTCOLUMNS(
'Sales Order', 
""Sales Order Number"",
'Sales Order'[Sales Order Number],
""Sales Order Line Number"",
'Sales Order'[Sales Order Line Number],
""Sales Amount"",
[Sales Amount]), 
'Date'[Date.Key0] IN {" +
GENERATE(EXISTING [Date].[Date].[Date].MEMBERS, 
[Date].[Date].CURRENTMEMBER.PROPERTIES("KEY"), ",")
+ "}),
[Sales Amount]>0)"

If this expression is used in an action and a user drills down on, say, the month April 2003, the following DAX query is generated and run to get all the Sales Orders for all the days in April 2003:

EVALUATE  
FILTER( 
CALCULATETABLE( 
SELECTCOLUMNS( 
'Sales Order',  
"Sales Order Number", 
'Sales Order'[Sales Order Number], 
"Sales Order Line Number", 
'Sales Order'[Sales Order Line Number], 
"Sales Amount", [Sales Amount]), 
'Date'[Date.Key0] IN 
{20030401,20030402,20030403,20030404,20030405,
20030406,20030407,20030408,20030409,20030410,20030411,
20030412,20030413,20030414,20030415,20030416,20030417,
20030418,20030419,20030420,20030421,20030422,20030423,
20030424,20030425,20030426,20030427,20030428,20030429,
20030430})
, [Sales Amount]>0)

OK, that’s more than enough for one post. In my next post I’m going to look at some of the shortcomings of this approach, how they can be (partly) worked around, and demonstrate a full solution for drillthrough on a regular measure and also on a year-to-date calculation.

Exploring The New SSRS 2017 API In Power BI

One of the new features in Reporting Services 2017 is the new REST API. The announcement is here:

https://blogs.msdn.microsoft.com/sqlrsteamblog/2017/10/02/sql-server-2017-reporting-services-now-generally-available/

And the online documentation for the API is here:

https://app.swaggerhub.com/apis/microsoft-rs/SSRS/2.0

Interestingly, the new API seems to be OData compliant – which means you can browse it in Power BI/Get&Transform/Power Query and build your own reports from it. For example in Power BI Desktop I can browse the API of the SSRS instance installed on my local machine by entering the following URL:

http://localhost/reports/api/v2.0

…into a new OData feed connection:

image

image

image

This means you can build Power BI reports on all aspects of your SSRS reports (reports on reports – how meta is that?), datasets, data sources, subscriptions and so on. I guess this will be useful for any Power BI fans who also have to maintain and monitor a large number of SSRS reports.

However, the most interesting (to me) function isn’t exposed when you browse the API in this way – it’s the /DataSets({Id})/Model.GetData function. This function returns the data from an SSRS dataset. It isn’t possible to call this function direct from M code in Power BI or Excel because it involves making a POST request to a web service and that’s not something that Power BI or Excel support. However it is possible to call this function from a Power BI custom data extension – I built a quick PoC to prove that it works. This means that it would be possible to build a custom data extension that connects to SSRS and that allows a user to import data from any SSRS dataset. Why do this? Well, it would turn SSRS into a kind of centralised repository for data, with the same data being shared with SSRS reports and Power BI (and eventually Excel, when Excel supports custom data extensions). SSRS dataset caching would also come in handy here, allowing you to do things like run an expensive SQL query once, cache it in SSRS, then share the cached results with multiple reports both in SSRS and Power BI. Would this really be useful? Hmm, I’m not sure, but I thought I’d post the idea here to see what you all think…

Creating A Partitioned Table In SSAS Tabular 2017 And SSDT Using M Functions

One of the coolest new features in SSAS Tabular 2017 and Azure Analysis Services is the integration of Power Query and M for data loading. Over the last year or so the Analysis Services team blog has posted a lot of fairly complex examples of how to use this functionality, but now that the latest release of SSDT has proper support for shared expressions I thought it would be a good idea to show a simple example of how to use it to create a partitioned table using M functions.

For this example I’ll be using the FactInternetSales fact table from the Adventure Works DW sample database, and the aim is to create a table in an SSAS Tabular project that has one partition for each year of data in FactInternetSales. Assuming that a new SSAS Tabular project has been created at the 1400 compatibility level with an integrated workspace:

image

…the first thing to do is to right-click on the Data Sources folder in the Tabular Model Explorer pane and select Import From Data Source:

image

This brings up the Get Data dialog:

image

Select SQL Server database and then click Connect. Enter the server name and database name in the SQL Server database dialog:

image

Choose how SSAS is to authenticate when it connects to the SQL Server database and click Connect:

image

Select the FactInternetSales table from the list of tables in the Adventure Works DW database:

image

This opens the Query Editor window; in it there is one query called FactInternetSales:

image

Here’s where it gets interesting. The first thing to do is to create a function that returns a filtered subset of the rows in the FactInternetSales table using the technique I blogged about here for Power BI. On the Query Editor menu bar, click Query/Parameters/New Parameter and create two new parameters called StartDate and EndDate that return the numbers 20010101 and 20011231. Here’s what they should look like:

image

image

These parameters are going to be used to filter the OrderDateKey column on the FactInternetSales table. Do this by clicking on the down arrow on the column header of OrderDateKey then selecting Number Filters and then Between:

image

In the Filter Rows dialog use the StartDate parameter for the start of the filter range and the EndDate parameter for the end of the filter range, then click OK:

image

Because the OrderDateKey contains dates stored as numbers in the YYYYMMDD format the result is a table that only contains sales where the order date is in the year 2001. This table should not be loaded into SSAS though, so right click on the FactInternetSales in the Queries pane and make sure that the Create New Table is not checked:

image

Next, on the same right-click menu, select Create Function:

image

In the Create Function dialog name the new function GetFactData then click OK:

image

The new GetFactData function will now be visible in the Queries pane; enter 20010101 for the StartDate parameter and 20011231 for the EndDate parameter and click Invoke:

image

This creates yet another new query called Invoked Function which should be renamed Internet Sales:

image

Right-click on this query and make sure Create New Table is selected. Next, click the Import button on the toolbar to close the Query Editor and load the Internet Sales table into SSAS.

At this point the Tabular Model Explorer will show all of the queries created above listed under the Expressions folder, and a single table called Internet Sales with a single partition:

image

Next, right-click on the Internet Sales table in the Tables folder and select Partitions:

image

This opens the Partition Manager dialog. Rename the existing partition to Internet Sales 2001:

image

Note that the M query for this partition calls the GetFactData() function to get the rows from FactInternetSales where OrderDateKey is between 20010101 and 20011231:

let
    Source = GetFactData(20010101, 20011231)
in
    Source

Click the New button to create new partitions, one for each year of data in the FactInternetSales table. Each new partition will initially contain the same M code shown above and should be edited so that the query gets data for the appropriate year:

image

Click OK, and the end result is a table with one partition per year:

image

What’s the point of using M functions to return the data for a partition, rather than the traditional method of using a SQL query embedded in each partition? One reason to do this would be to make maintenance easier: if you need to do something like add a new column to a fact table, rather than editing lots of partitions you just need to edit the function and all the partitions will reflect that change. I can think of a few others, but I’ll save them for future blog posts…

SSAS Multidimensional HOLAP Storage: Even More Useless Than You Might Think

In almost 20 years of using Analysis Services I have never, ever used HOLAP storage. However the other week I was with a customer that was using ROLAP storage on top of Exasol and while query performance was generally good, I wondered whether building an aggregation or two in SSAS might help query performance in some cases. Surely HOLAP could be useful here? Sadly not.

What I hadn’t realised was that when you use HOLAP storage and process a partition, SSAS generates exactly the same fact table-level SQL query that is used to process a MOLAP partition. It then uses this data to build any aggregations you have defined and after that throws the data it has read away, leaving only the aggregations stored in MOLAP mode. Therefore you get exactly the same, slow processing performance as pure MOLAP storage and worse query performance! It even executes the SQL query when there are no aggregations defined. I had assumed SSAS would generate one SQL query for each aggregation and get just the summarised data needed by the aggregation but I was wrong. This means that for the kind of scenarios where ROLAP on a fast relational database is becoming more popular (for example when working with large data volumes and/or real-time data) HOLAP is not a viable option.