Filtering Tables Dynamically in DAX

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Sometimes, your DAX calculated measures might need to filter a table dynamically based on a certain condition. For example, you might have a Type 2 table like this one:

ClaimID

ClaimDate

ClaimStatus

RowStartDate

RowEndDate

XXX-1

1/1/2015

Open

1/1/2015

1/15/2015

XXX-1

1/1/2015

Approved

1/16/2015

12/31/9999

When a change is detected on the existing claim, this design expires the previous row and adds a new one. A common business question would be “How many claims do we have as of a given date?” Tabular is more flexible than MD answering this question because you can directly filter the table. In your first attempt, you might write the following calculated measure:

ClaimCount:=CALCULATE(DISTINCTCOUNT([ClaimID]), [RowStartDate]<=[FilterLastDate] && [FilterLastDate]<=[RowEndDate]))

Where FilterLastDate is another calculated measure that returns the max date if the user has selected a date range, such as an entire month from a Date hiearchy, so that the measure is evaluated as the last date of the user selection. However, this attempt fails with the error “A function ‘CALCULATE’ has been used in a true/false expression that is used as a table filter expression. This is not allowed.” This article provides more context although I personally believe that the explanation doesn’t give all the details as the second argument is Boolean in this case. To fix this you need a more complicated expression that uses the FILTER function:

ClaimCount:=CALCULATE(DISTINCTCOUNT([ClaimID]), FILTER(ALL(ClaimSnapshot[ClaimDate], ClaimSnapshot[RowStartDate], ClaimSnapshot[RowEndDate]), [RowStartDate]<=[FilterLastDate] && [FilterLastDate]<=[RowEndDate]))

The FILTER function does the same filtering logic. If the table you filter on is related to a Date table, such as on ClaimDate, you need to ignore its context. Otherwise, the calculated measure scope will be limited by the Date selection. To do so, you need to use the ALL function but because it returns a table, the result needs to include all columns that you need to filter on.

Finding Duplicates in DAX

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A prerequisite for creating a relationship in Tabular/Power Pivot is to have a primary key column in the table on the One side of the relationship. This column must have unique values. If it doesn’t, the relationship won’t get created and you’ll get an error that the both tables have duplicate keys. If you have a relatively large table, it might be difficult to find the duplicates.

ID

Column1

1

Foo

2

Foo

1

Foo

 

However, given the above table design, you can add a simple calculated column to the table to return the count of duplicates for column ID using the following DAX formula

=CALCULATE (COUNTROWS(), ALLEXCEPT(Table1, Table1[ID]))

This expression uses the COUNTROWS() function to count the number of rows of Table1. Coupled with the CALCULATE function, this expression will be resolved in the context of every row. To ignore the column that you want to count on (ID in this case), you need to exclude it from the context, so that the row counting happens across the entire table for each ID value. Once the column is created, you can filter on it in the Data View to find out the duplicate rows with values 2, 3, etc.

My Wish List for SQL Server.vNext

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In an attempt to give customers more transparency, Microsoft recently published a Cloud Platform Roadmap. The product groups are also actively seeking feedback for the on-premise products (also known as boxed products). For example, if you have subscribed to the Power BI.vNext public preview, you can use the BI in SQL vNext forum to provide feedback (not sure why there instead of on connect.microsoft.com).

So, here is my open high-level SQL Server.vNext wish list:

  • SSAS – Merge Multidimensional and Tabular and take best from both. I like the in-memory engine and flexibility of Tabular but at the same time I miss the MD pro features. To put this in perspective, I’d like to see the following features added to Tabular:
    • Additional relationship types, such as M2M relationships (it looks like this will happen judging by the Power BI features), multi-grain relationships (joining to a table at a higher grain than the key), role-playing
    • Scope assignments
    • Sets
    • MDX support for business calculations – BI pros have been learning MDX for the past 15 years so this knowledge shouldn’t be wasted. Besides, some constructs are better expressed in MDX not to mention that Tabular doesn’t have support for hierarchy navigation.
    • Enterprise scale features – parallel partition processing within a table, ability to define which columns will be hierarchized (measures typically shouldn’t, yet now every column is hierarchized), compression on calculated columns
    • Removal of DirectQuery limitations
    • Custom (non Windows-based) security – This applies to both MD and Tabular in order to allow developers to embed reports in custom applications.
    • Better toolset – No matter how good SSAS gets, it won’t go far if there is no good client support. Excel and Power View need catching up. For example, Excel need to generate DAX natively, optimize MDX queries (especially for detail-level reports), and add Power View support for MD, plus numerous enhancement to catch to modern interactive tools.
    • Tabular Designer enhancements – it’s painful to wait SSDT to refresh after every step.
  • SSRS
    • Report Designer should continue where it left off in 2010 when focus was shifted on Power View. See top requested features on connect.microsoft.com, especially in the area of report parameters.
    • Power View – conditional formatting, drillthrough, SSAS action support, mapping enhancements (region coloring, point-to-point mapping)
    • Ability to embed Power View reports in custom apps.
    • Data alerts on Power View and SSRS in native mode.
    • Q&A on prem
    • Bring Power BI features to boxed products. Since we decouple Power BI from SharePoint, installing it on a local IIS server shouldn’t be an issue.
  • SSIS – Project mode and development enhancements in 2012 were great but the product group should take a look at competing products, especially those that attempt to automate ETL. I don’t care much about the Data Flow since I typically use the ETL pattern, so I won’t comment on the data flow tasks.
    • Data profiling should be built in the data sources instead of separated as a separate task
    • Change management – make it easy to see what source mappings have changed. Don’t make me go through input and output connectors to fix these mappings when they change.
    • Scale out ETL across multiple servers
  • SQL Database Engine – Based on what I do, I need better support for data warehousing.
    • Improve query optimizer for large joins
    • Unify memory technologies – in most cases you want to have both in-memory tables and fast analysis.
    • Enhance clustered columnstore indexes to support additional regular indexes. See my post for more info.
  • MDS/DQS
    • Ideally, unify MDS and DQS into a single product as there is a significant overlap.
    • MDS Excel add-in is good but usability needs to be improved. No one wants to scroll a long pick list of a domain-based attribute to find something.
    • Ability to reference an entity from another model.

Microsoft is Serious about Statistical Analysis and Machine Learning

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Microsoft announced two company acquisitions related to data analytics.

It announced that it will acquire Revolution Analytics. Revolution Analytics is the leading commercial provider of software and services for R, the world’s most widely used programming language for statistical computing and predictive analytics. This acquisition could help more companies use the power of R and data science to unlock big data insights with advanced analytics.

Previously, Microsoft also announced that it will acquire Equivio. Equivio is a provider of machine learning technologies for eDiscovery and information governance to help customers tackle the legal and compliance challenges inherent in managing large quantities of email and documents.

Demystifying Clustered Columnstore Indexes

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Non-clustered columnstore indexes (NCCI) were introduced in SQL Server 2012 to improve the performance of large aggregate queries (common for data warehousing) with the caveat that there were read-only. Consequently, the ETL process has to drop NCCI, load the data, and recreate the columnstore index.

NOTE Building an index (columnstore or regular) should be a highly-parallel operation. Building a columnstore index in particular should max out all licensed cores. Currently, we have an open support case with Microsoft where a columnstore index allows adding a computed column (while it shouldn’t). Consequently, SQL Server builds the index using a single thread which may lead to excessive index creation times.

SQL Server 2014 introduced clustered columnstore indexes (CCI) which offer two main advantages:

  1. CCI is updatable — Therefore, you don’t have to drop and recreate the index anymore.
  2. Storage is greatly reduced — For example, you might have a fact table of 100 GB. Assuming x10 compression, your table space with NCCI will be 110 GB. However, if you create CCI the table space will be only 10 GB. This is why Analytics Platform System (previously known is PDW) uses CCI.

On the downside, CCI doesn’t support any other indexes that you might need to optimize ETL or speed up joins. Basically, CCI is the only index you can have on a table. However, CCI is not designed for equality and short-range queries that are typical for detail-level SELECT or MERGE queries. It’s a common misconception that you don’t need such indexes with CCI but this is not the case. I hope a future release of SQL Server enhances CCI to support regular indexes as well.

Presenting at Atlanta.MDF

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I’m presenting at the Atlanta.MDF group on Monday, January 12th. I’ll be covering a wide range of tips and techniques for analyzing and improving performance of SQL Server-based data analytics solutions. Hope you can make it.

Title: Can Your Data Analytics Solution Scale?

Abstract: Does your ETL exceed its processing window? Do your users complain about the SSRS spinny? Can your SQL Server database design deliver the expected performance? Can the system scale to thousands of users? Join this session to learn best practices and tips for isolating bottlenecks and improving the performance of data analytics solutions. I’ll dissect the layers of a “classic” solution (relational database, ETL, data model, reports) and share solutions harvested from real-life projects to address common performance-related issues. 

SQL Server and 20 Cores Limit

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Scenario: You execute a SQL Server 2012 task that uses parallelism, such as index rebuild or a query on a server with more than 20 cores running SQL Server 2012 Enterprise Edition. In the Windows Task Manager, you observe that the task uses only 20 cores. We discovered this scenario during a rebuild of a columnstore index. To confirm this further, you examine the SQL Server log and notice that a similar message is logged when the SQL Server instance starts:

“SQL Server detected 8 sockets with 4 cores per socket and 4 logical processors per socket, 32 total logical processors; using 20 logical processors based on SQL Server licensing. This is an informational message; no user action is required.”

Explanation: More than likely, you have upgraded to SQL Server 2012 from SQL Server 2008 R2 under Software Assurance. Microsoft created a special SKU of Enterprise Edition to support this scenario with the caveat that this SKU limits an instance to using only 20 processor cores (or 40 CPU threads if hyperthreading is enabled). If this level of parallelism is not enough, the only solution is to switch to the Enterprise Edition SKU that is licensed per core and purchase a license that covers as many cores as needed. Once you obtain the new license key, you can upgrade your SQL Server instance:

Setup.exe /q /ACTION=editionupgrade /INSTANCENAME=MSSQLSERVER /PID=<PID key for new edition>” /IACCEPTSQLSERVERLICENSETERMS

Tabular M2M Relationships on the Horizon

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One of the biggest strengths of Microsoft self-service BI is the ability to create sophisticated data models on a par with organizational BI models built by professionals. This fact is often overlooked when organizations evaluate self-service tools and the decision is often made based on other factors but not insightful understanding of the data model capabilities. This is unfortunate because most popular tools on the market don’t go much further than supporting a single dataset. By contrast, Power Pivot allows you to import easily multiple datasets from virtually anywhere and join the resulting tables as you can do in Microsoft Access. This brings tremendous flexibility and analytical power.

Unlike multidimensional cubes, one of the limitations of the Power Pivot and Tabular data models has been the lack of support for declarative many-to-many relationships. The workaround has been using a simple DAX formula to resolve the relationship over a bridge table, such as =CALCULATE (SUM (Table[Column] ), <BridgeTable>) but this approach might present maintenance issues, as you have to create multiple calculated measures to support different slicing and dicing needs. However, as pointed out in my latest newsletter, the upcoming version of Power BI aims to remove adoption barriers and adds new features. And, one of this features, is bidirectional relationships and declarative support of M2M relationship, which Chris Webb already wrote about.

To test the M2M relationship, I attempted to create the same M2M scenario that I used in my book, which models a joint bank account. The corresponding Power Pivot schema is shown below. The CustomerAccount table is the bridge table that resolves the M2M relationship (a customer might have many accounts and a bank account might be shared by multiple customers). The Balances table stores the account balances over time and the Date table lets us analyze these balances over time.

010415_1902_TabularM2MR1

Setting up a M2M relationship in the Power BI Designer is achieved by changing the “Cross filter direction” relationship setting to Both. This setting and bi-directional relationships are described in more details here.

010415_1902_TabularM2MR2

Indeed, creating a report that shows balances by customer resolves the M2M relationship and aggregates correctly.

010415_1902_TabularM2MR3

Unfortunately, attempting to slice the report by Date returns an error in the preview version of the Power BI Designer so the M2M feature is still a work in progress. Brining this further, a useful addition could be declarative semi-additive functions to allow the user to set the aggregation behavior of the Balance measure, such as to LastNonEmpty. Similar to Multidimensional, this will avoid the need for user-defined explicit measures.

Getting ETL Task Duration

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Happy New Year!

ETL exceeds the processing time window? Optimizing ETL, starts with obtaining task-level execution times? If you use SSIS 2012 project deployment mode, task-level stats are already loaded in the SSIS catalog and you can use the following query:

SELECT execution_id,

CASE WHEN [status] = 1 THEN ‘created’

WHEN [status] = 2 THEN ‘running’

WHEN [status] = 3 THEN ‘canceled’

WHEN [status] = 4 THEN ‘failed’

WHEN [status] = 5 THEN ‘pending’

WHEN [status] = 6 THEN ‘ended unexpectedly’

WHEN [status] = 7 THEN ‘succeeded’

WHEN [status] = 8 THEN ‘stopping’

WHEN [status] = 9 THEN ‘completed’

END AS [status_text],

DATEDIFF(ss,start_time,end_time) DurationInSeconds

FROM catalog.executions e

What if you are not on SSIS 2012 or later yet or you are not using the project deployment mode or a framework that logs the task duration? You can still obtain the task duration but you need to enable SSIS logging for each package you want to monitor, as follows:

  1. Open the package in BIDS/SSDT.
  2. On the SSIS menu, click Logging. Configure logging to use the SSIS Log Provider for SQL Server. The provider will save the statistics in a SQL Server table so you can easily query the results.010215_2129_GettingETLT1
  3. On the Details tab, select the OnPreExecute, OnPostExecute, and most importantly the OnProgress event so you can get the same level of execution statistics as in the BIDS/SSDT Progress tab.010215_2129_GettingETLT2
  4. Once you configure the SSIS Log Provider for SQL Server, it will create a sysssislog table in the database you specified when you configured the provider. When the SQL Server Agent executes your package, you can use a query like the one below to obtain task-level durations:

    SELECT executionid Execution,

    PackageName = ( SELECT TOP 1 source FROM dbo.sysssislog S WHERE S.executionid = L.executionid AND S.[event] = ‘PackageStart’ ),

    PackageStep = l.source,

         Runtime_min = DateDiff(minute, MIN(L.starttime), MAX(L.endtime)),

    Runtime_hr = DateDiff(hour, MIN(L.starttime), MAX(L.endtime)),

    StartTime = MIN(L.starttime),

    EndTime = MAX(L.endtime),

    FinishDate = CAST(MAX(L.endtime)AS DATE)

    FROM dbo.sysssislog L WHERE L.[event] != ‘PackageStart’
    GROUP BY executionid, L.source

2015 Annual TI Forecast by TEKsystems

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TEKSystems has been a wonderful sponsor of the Atlanta MS BI Group. They’ve recently published an interesting 2015 Annual TI Forecast report. According to the report, Business Intelligence/Big Data will be among the top most impactful technologies in 2015. More key facts:

  • Seventy-one percent of IT leaders report confidence in their ability to satisfy business demands in 2015, representing an increase from 66 percent and 54 percent in forecasts for 2014 and 2013, respectively.
  • The top five areas where most IT leaders expect to increase spending in 2015 include security (65 percent), mobility (54 percent), cloud (53 percent), BI/Big Data (49 percent) and storage (46 percent). Twenty-nine percent of IT leaders also expect to increase spending on ERP.
  • Seventy-three percent of IT leaders indicate that operational objectives such as reducing costs, improving efficiency, consolidating, standardizing and streamlining present the biggest organizational challenges.
  • Salary increases are most likely to be average, with 68 percent of IT leaders saying that they expect overall staff salaries to increase by up to 5 percent. Only 8 percent expect increases of 6 percent or more and 21 percent expect salaries to remain the same.
  • Hiring expectations have also slowed. Entering 2014, 47 percent of IT leaders expected an increase in full-time IT staff hiring. Entering 2015, just 40 percent expect an increase, and 50 percent expect it to be the same as 2014.