We have sold specific quantities of products. Can we look at a week for a year in a slicer and see the percentage of items sold for each day. Which days do we sell the most products overall?
We have the following model (Just the parts that will be required for this exercise
And thanks to the Power BI Forums for giving me some help on figuring this out.
What we want to end up with is:
A year Slicer
Product category on rows of a matrix
The Day Name from Date on the Columns of the Matrix
And % Quantity for that day based on all the days of the week as the value
Power Query Editor
At first I believed that I needed to add some kind of Ranking order for the DAX to use and as this will be a column its better to do in Power Query Editor (Or in the Sort DB)
To speed things up I created a Year Week Column in SQL DB consisting of the following examples
So the weeks 1 to 9 was padded out with a zero. I then formatted this to a number field and called it Year Week. Every seven rows within that week in the date table will have the same Year Week Number Applied
I can now create the measure. Lets have a look at it in a bit more detail
Order Quantity by Week % = Var varOrderQtyWeek = CALCULATE(SUM(FactResellerSales[Order Quantity]), FILTER(ALL(DimDate), DimDate[Year Week])) RETURN DIVIDE(SUM(FactResellerSales[Order Quantity]), varOrderQtyWeek)
And this measure is then set as a percentage.
First of all we create a variable. It gets the Sum of Order Quantity and it filters by using an ALL on the column Year Week we just created in the Date Table
“ALL Returns all the rows in a table, or all the values in a column, ignoring any filters that might have been applied (On Year Week).”
And we return the sum of order Quantity (Which in the context is just for, for example Friday and Accessories by the Sum of Order Quantity
This appears to work
We have Implicitly filtered by Product Category and Day Name of Week.
the question here is, did we even need to set ALL on Year Week column in date. Could we have just said use the entire date
Order Quantity by Week % = Var
varOrderQtyWeek = CALCULATE(SUM(FactResellerSales[Order Quantity]), ALL(DimDate))
RETURN DIVIDE(SUM(FactResellerSales[Order Quantity]), varOrderQtyWeek)
This is working in the same way and makes sense to me. We are using all the dates in the date table. And removing the Filter will create a faster DAX query.
Its looking at the entire data set and we can see that everything totals to 100%. So for us, taking into account all years Thursdays look like a good day especially for accessories.
However we don’t want to analyse the full data set and when we add in a year slicer the logic fails
As you can see, the story is still true but its telling the wrong story. Now for Accessories we have 31% of sales happening in 2021, attributing to smaller percentages across the days.
So we want to change the DAX to accept the Year Slicer
Order Quantity by Week % =
Var VarALLEXCEPT = CALCULATE(SUM(FactResellerSales[Order Quantity]), ALLEXCEPT(DimDate,DimDate[CalendarYear]))
DIVIDE(SUM(FactResellerSales[Order Quantity]), VarALLEXCEPT)
And this appears to now work just taking the year 2012 into consideration because we are using ALLEXCEPT
Thursday is definitely a good day.
“ELLEXCEPT Removes all context filters in the table except filters that have been applied to the specified columns.”
So we create a variable to get the Sum or Order Quantity with ALLEXCEPT our Date Slicer which in this case is the calendar year slicer
So we are using 2012 from the date Dimension in the slicer. And Bikes from Product and Thursday as the Week Name from date in the Matrix
We Divide the Sum of Quantity which has all the filters applied. Bikes. Thursday. 2021
By the Sum Of Quantity with all, Exceptwe do apply the Calendar Year.
50 is Bikes on a Thursday in 2012
100 is Bikes in 2012
DAX is something I do struggle with a little. You think you understand it. Turn your head from the screen and its gone again.
But hopefully this goes a little way to understanding how this DAX in this specific context has been approached
Lets break the above down a little to understand what is happening
VAR VActivityDates = SELECTCOLUMNS(DimDate,”Dates”, DimDate[DateKey])
First of all create a variable. SELECTCOLUMNS
“Adds calculated columns to the given table or table expression.”
We start with the table they come from. then we give the name to the column in SELECTCOLUMNS “ColumnName”, Next comes the expression which in this case is the column reference.
VAR VDates = CALENDAR(MINX(DimDate,DimDate[DateKey]),MAXX(DimDate,DimDate[DateKey]))
Next comes the VDates Variable. Calendar Returns a table with a single column named “Date” and it contains a contiguous set of dates. We need to provide the range of dates. In this case MINX finds the earliest date and MAXX finds the Maximum date in our date dimension
Now this should work with our slicer. In this case Min 01/09/2021 Max 30/09/2021
And now we get to the measure that will be RETURNED
“INTERSECT A table that contains all the rows in table_expression1 that are also in table_expression2”
COUNTROWS simply counts the number of rows within a table or an expression
So here we can see the intersect and if working together. If there are rows counted (True – There are rows then 0 else 1.
Still Struggling to understand? Me too. Lets draw it
Here is where I am a little confused. I’m not sure which part of the DAX works with the slicer. SELECTCOLUMNS or CALENDAR MINX MAXX? I’m making the assumption that CALENDAR takes the min and max of the slicer but its incredibly difficult to test so if anyone has any more insight on this that would be fantastic.
And we can now look at everything together in a report
We have used Is Not =1 in the ‘Is not in the Date Filter’ as out value and its always ever 0 or 1
But now we are asked another business question
How MANY reports did we not view in the current date slicer?
with the measure as it stands. It needs the Report Name or the Data set name to provide details
We can’t use what we have in a card because we cant add the implicit filter (Report Name etc).
So How can we do this one?
We can solve it using variables
Total Reports not in date Filter =
//Clear all filters which are applied to the specified table.ALLCROSSFILTERED
var VAllReports =CALCULATE([# reports],ALLCROSSFILTERED(DimDate))
//Total within the date filtervar
VInFilter = [# reports]
//All reports - Reports inside the slicer
Using ALLCROSSFILTERED brings back the total reports 4 as it removes all the filters
then we get back the total of reports in the date slicer and finally take in filter away from all the reports.
Out # reports is a measure made from distinct report IDs already. We now have everything we need to create these reports thanks to DAX.
Imagine the scenario. You are dealing with two dates. date A and B. You create an active and an inactive relationship to your date table.
You can create Dax with USERELATIONSHIP for any measures that use the inactive join. Great for the bar charts, line charts etc.
But what if you have a slicer for Year on the report? At the moment that slicer is connected to Date A because you simple drag year from the date table.
This report needs to be sliced against Date B. Is there a way to do this?
Lets look at one of our measures that uses USERELATIONSHIP
YTD Measure =
CALCULATE(TOTALYTD([Number of Records],’Date'[Date]), USERELATIONSHIP(Metrics[DateKeyB],’Date'[DateKey]))
The USERELATIONSHIP can only be used with CALCULATE,CALCULATETABLE, CLOSINGBALANCEMONTH, CLOSINGBALANCEQUARTER, CLOSINGBALANCEYEAR, OPENINGBALANCEMONTH, OPENINGBALANCEQUARTER, OPENINGBALANCEYEAR, TOTALMTD, TOTALQTD and TOTALYTD
From this it is clear you can only use it in a measure with a metric.
And you cannot use a Measure in a slicer. Slicers have to be created from a column.
Which means that our inactive dates can’t be used in a slicer. And this is problematic because if you have a page of time based visuals all using the USERELATIONSHIP then its a fair shout that you are going to have a slicer too for example ‘Year’
So can we come up with a workaround?
Workaround 1. Adding date information to the fact table
Out model rules are
DateKeys in the Fact table. I also hold the dates hidden just in case
The dateKey Joins to the date Dimension which contains Year, Day, Month etc
So what I am going to do in this case is add my relationship B details into the fact table just for the time being.
s.[DateB] AS [Date B],
DATEPART(Year,s.[DateB]) AS [Year B],
DATENAME(Month,s.[DateB]) AS [Month B],
DATEPart(Month,s.[DateB]) AS [Month No B],
[staging].[fnQuarter](s.[DateB]) AS [Quarter B],
I have created a Quarter function with the specific quarter logic which is use for every Quarter period.
This is then refreshed into the Power BI Dataflow
And then refreshed into my data set.
All ready to work with. What I decided to do in Power BI was create a table containing those values.
Support End Date (For Slicers) =
SUMMARIZE ( 'GrowthHubMetrics',
'GrowthHubMetrics'[Support End Quarter],
'GrowthHubMetrics'[Support End Month],
'GrowthHubMetrics'[Support End Month No],
'GrowthHubMetrics'[Support End Year],
'GrowthHubMetrics'[Support End Date])
The dates in the fact table were then hidden leaving the above Slicer table.
And then I remembered that Date time Measures don’t work without a continuous date table and DateB isn’t continuous.
But then I remembered that I had already put in a lot of work creating all the date time measures on the inactive join to the date table using USERELATIONSHIP so actually all the date time measure are fine.
Would I go back and create a date table for dateA and a date table for DateB so I can have slicers and drill down to the date. Its very possible but that renders the use of USERELATIONSHIP Pretty null and void, unless you still want to slice these visuals against DateA.
Connect the DAX table to the model.
the date Table for Slicers is connected up to Dimdate in the model and we are ready to go
So all the measures are still connected to the date table through the inactive join
But the slicer can be set up over the new DAX table
I’m hoping to get a better way of doing this as we go because it seems that you should be able to do this without having to create another table.
In the end, this became so complex and issue heavy (Drill throughs not working properly etc) I gave up. Created a reference of the date table for Date B. Connected this up. removed the DAX table and changed all my measures to get rid of USERRELATIONSHIP.
So Pages 1 to2 use DateA and Pages 3 and 4 use DATEB.
As a conclusion, if you are wanting to use Drill through and Drill down I think I would recommend role playing dimensions. the complexity of the USERELATIONSHIP with just seems incredibly complex at the moment.
Its a shame because I love the idea of switching to a none active join but in practice its proved unworkable.
The analysis is performed at the record level of the ‘table’ A field in explain by is not on the ” table or a table from the same data source and related to it by a many to one relationship. Try Summarising it
This model is all about behaviour and attitudes for an event company who put on IT events for companies who want to learn more about cloud based solutions.
The stakeholders are all the people who go on the courses, and those people who arrange the courses.
Its important for the company to know how their customers are reacting to their cloud based events and training. Which ones are doing well or not in terms of reactions.
The trainer or presenter sends out a questionnaire after ever event / course. they also send in their own questionnaire about how they felt the course was engaged with.
I have a Star Schema and in one of the dimensions I have a behaviours table. We want to know what influences behaviour from all the other attributes from around the star schema
There can only be a certain number of behaviour types so this dimension is set as a junk dimension. Each Type of behaviour is joined to the other using a cartesian Join
Every behaviour type is matched to every other behaviour type and then we can simply assign the correct row to the person event and theme
So a stakeholder can go to many events
A stakeholder can hold different behaviours for every event
We want to see what effects behaviour, so the Key Influences visual is the one we really want to use in this project
In this visual we are analysing by Explain by.
Add in a measure from the fact table and it works fine
But this isn’t telling us anything. We need descriptive information from the other dimensions
So lets go for something from Events
And here is where we get the error
The analysis is performed at the record level of the ‘table’
Obviously this part of the error makes sense because we want to understand the behaviour
A field in explain by is not on the ” table
That is correct. we are explaining by a field in another dimension
or a table from the same data source and related to it by a many to one relationship.
Try Summarising it
How to deal with this issue
the error doesn’t give much away but the solution lies in the model.
The recommended single direction join has been used on every single relationship. Therefore, the dimension can filter the fact but the fact cant filter the dimension.
And specific to this model, Another dimension cant filter another dimension
Events and behaviour cant filter eachother.
Unfortunately setting all the relationships to both didn’t resolve the issue either. Maybe the answer lies with DAX
Lets look at that error again
the Keyword in the error is SUMMARISE.
Now we know exactly what we want to use as the ‘Explain by’ Lets see if we can set up a Summary table using DAX
Calculation groups look like a game changer, but are they? These have been available for Analysis Services tabular models for a while. Now Tabular editor Lets you build calculation groups for Power BI.
Taking one of our current pbix files as an example.
There are metrics for number of events, Financial metrics, timing metrics. Each one has to be added to Year to Date, Last month, last Year, Month to date etc metrics.
The same measures are repeated over and over again for the different metrics in the report.
And adding metrics in Power BI desktop isn’t a fast process. Its actually quite fiddly so adding the first lot of DAX required always takes a lot of time.
As from July 2020 you can reach tabular editor Via External tools
You must have them installed at the right version for this to work.
You must enable Store datasets using enhanced metadata format in Options > Preview features
You are taken straight to the model you are connected to
Right click on Tables. Create New and Calculation Group
The best example to look at is time intelligence
This example is renamed to time Intelligence. What has been created is essentially a single column table.
the rows are based on all the calculation items that I already have in this model.
I initially recreate all the metrics from source as SUMs so they can be used within measures. Along with this I may have other base calculations like Distinct Count of IDs to make a number of events. Minimum, Maximum, Average etc.
right click Calculation items and choose new calculation item
In this example, go back to the original pbix and copy a time intelligence DAX measure
Total Sales is a measure created with SUM() using the Sales Amount metric from the data source
The measure is replaced with the scalar function SELECTEDMEASURE()
Instead of having to recreate this DAX over all your ID’s where necessary you only need to do it once
Scalar function – a function that returns one single value
The base DAX in this data set can now be added into Tabular Editor
You can imagine starting a prototype model with DAX for a specific metric. Then recreating as calculation groups so you can add all your other metrics without having to copy and paste the same measures over and over again
Tabular Editor currently has no intellisense so you wouldn’t write and test your DAX in here. this would be done in Desktop. If you wrote incorrect DAX in here and Saved to Power BI, you would then see an error icon in Tabular Editor.
Adding more time Intelligence from the original report
The rows are based on all the calculation items that are already have in this example model.
However the DAX needed to be amended because previously the Year to date measure was used to create variance (Two separate measures). We need to be able to give each measure the underlying measure by using variables in order to use them successfully.
So for example
YTD Sales Var % = DIVIDE([YTD Sales Var],[LY YTD Revenue])
Note that YTD Sales var and LY YTD Revenue Measures have already been created over the original year to date measure. We cant have this so we need to move to
YTD Sales Var % = VAR CY = [Total Sales]
VAR TYTD = TOTALYTD([Total Sales],DimDate[FullDateAlternateKey])
VAR LYTD = CALCULATE(
VAR VYTD = TOTALYTD([Total Sales],DimDate[FullDateAlternateKey])-
Within this measure we call the base measure and create the variance% by calling variables.
Now these time Intelligence measures can be created in Tabular Editor
Notice that you cant use another variable within a variable. So our Total year to date has to be re added within the last year to date measure.
If we were doing this without calculation groups in mind we would simply reference the year to date measure we had created
Again, Notice how we cant reuse a variable within a variable. So LTYD needs the full DAX inside the SAMEPERIODLASTYEAR DAX.
And Year to Date variance requires both last year to date and total year to date. this makes your DAX more complex than simply using a measure already set up.
In the above instance I could take out TYTD Variable but honestly. Im leaving it there as a reminder of what the DAX is for Year to Date
As you can see, each measure uses one base measure
And for the percentages I added format String Expression “0.00%”
Save the calculation group into the main desktop file
Lets see the calculated measure group in action using a matrix
Name from the time Intelligence group has been added to columns on the matrix.
Year and Month are in Rows
Total Sales, the base measure has been added to values
Name has also been added to a Slicer so you can turn off those you aren’t interested in.
To me, the big win of calculation groups is being able to create one measure and using it across multiple measures instead of creating the same measure over and over again.
And quickly switch to quantity by adding that measure to value
Issues with using calculation groups
formatting each item is much more difficult in tabular editor because you have to know the code. There is no help for creating these expressions.
Similarly, you cant develop DAX Here, you need to do it first within power BI Desktop
Your DAX has to become much more complex, rather than creating a measure and then referencing this measure within another measure. Like Year to Date and Last Year to Date
You cant create the matrix with Months in columns
This is using the measures created in the data set. As you can see, the Months are shown as columns and the measures are also displayed
You cant do this with column groups.
Lets have a look at some visuals already created with time Intelligence to see if we can recreate
Variance Waterfall chart
This is an example of a waterfall variance chart for year to date. If we didn’t have measures outside of a calculation group, could we still pull off the exact same solution?
Table: No you cant recreate the table. You would have to move to a matrix
With a filter on name to the measures you are interested in. It doesn’t appear that you can turn off grand totals though so we have some information there that we don’t need. the Total column.
So, ok but not great
Waterfall visual; there doesn’t appear to be any way you can recreate this. so to create my variance visuals there has to be a measure that can be used.
Calculation groups seem to only for for one visual. the Matrix. Where you can add the base measure to values and the Name to columns.
Even the matrix cant be fully configured to how it would normally be shown with months in columns and the measures underneath.
In order to use time intelligence for all other visuals, there still needs to be measures in your model to use.
It would be a great idea if you could fully get rid of your duplicated measures but you cant.
Because of this, I still don’t have the results I need to spend time creating calculation groups.
Other people seem to be seriously excited about this though so maybe I am missing something. Please let me know if I am, I would be very interested to get another point of view
We are looking at a Star Schema with a Date table connected to the Fact table by Order date Key
for these examples, the active relationship is the only one that matters
Lets have a look at all the issues arising from using the Date table without marking at a Date table
Date Slicer seems to remove the report filter flag for the last 3 years
Rolling 3 year flag= IF(DATEDIFF('Date'[Date].[Date],TODAY(),YEAR)<=3 && DATEDIFF('Date'[Date].[Date],TODAY(),YEAR)>=0,1,0)
This flag has been added to the entire report and set to 1 to make sure there is only information from these 3 years
If I add date as a table I get 2017 2018 2019 and 2020 as expected for a rolling flag.
However As soon as I change that table into a Slicer, all the years appear in the data set.
In this case from 2016. The filter stops being applied on the slicer
DAX FUNCTION SAMEPERIODLASTYEAR and the date hierarchy
We have some DAX to create SAMEPERIODLASTYEAR.
This is the DAX
LY Total = CALCULATE([Total],SAMEPERIODLASTYEAR('Date'[Date].[Date]))
Note the .[Date] at the end. Because we are using the date hierarchy to create the measure you can choose which level of the hierarchy to use. In this case we are saying we want the date level.
This will come back later
This is used in a visual and we have added Month Year which is a column in the date table.
As you can see, last year displays exactly the same as the current measure. This does not work
it works using the DateTime Hierarchy in the visual? However in this instance this date time hierarchy isn’t required. We don’t want the user to have to drill down to month from year every time.
In this example, the only field you can use for any measure that is date time specific is the date field
Mark as Date time
Always make sure you have a date table connected to a fact table
Note that the Date is now not connected to a back end hierarchy table.
Marking as Date table means that all your data within this table can be used for Date Measures
However lets look at the DAX that was created
All the Lat year measures are now erroring. this is because of the .[Date] at the end of the DAX
The date does not contain a hierarchy any more so if you have used .[Date] This needs removing. Its specifically related to the hierarchy.
A Year to day hierarchy has been created in the date table. This means that you have created a more compact data model and saved space.
And you can now use Month Year on the Axis
Date Table is Marked. How to work with it
This is part of the star schema in Power BI
Now the date table is marked as date, the Date hierarchy table is removed for Date within the Date table. this saves space and you can simply create your own date hierarchy to work with
The Active Join is on Received Date
All my measures so far are based on received date
Each Date in the fact table creates an extra date table to produce the hierarchy. So to save space, you should create inactive joins to the other dates and then remove the dates in the Fact table leaving just the keys. the model should then reduce in size
This works great for the measures. I can create measures based on the none active ones and simply choose to USERELATIONSHIP
LY Totals by Closed Date = CALCULATE([Total],USERELATIONSHIP('Complaint Metrics'[Closed Date Key],'Date'[Date Key]),SAMEPERIODLASTYEAR('Date'[Date]))
The above is an example of using the Closed Date None active join for Last years Totals
So i can have measures for Received this Year, Received Last year and Closed this year , Closed Last year (For Example)
This is all absolutely spot on. However there is more logic we need to think about. What about when the users want to create a drill through
This visual was created on the active relatioship so its recieved date
However your users may want to drill through to the following
how to do this?
Currently you may have the Active join on received date and Inactive on Start and Closed date
In my example, I have also kept the dates in the fact table along with the Date Keys for each Date.
Because they are in the fact table they all have date hierarchies.
Remove the Date Hierarchies across your entire dataset
You could keep them there and simply remove their hierarchies
File > Options and Settings > Options
You can turn off time intelligence for the specific report OR globally. the recommendation is to actually do this globally when you use a date table
This way you can use the dates in the fact table for drill down without creating unnecessary data with the date hierarchies
Role Play dimensions
If you want to drill down to all your dates on a regular basis, AND if there isn’t one main date and other dates that are not used as often.
In Power Query Editor go to your date table and create a reference table for each date
In this case the Date table has been referenced once and is named date created. date as been renamed to date Engagement
with this set up, there is only one join to each date key so no inactive relationships.
Any DAX you create can reference the correct date tables and your Dates can be removed from the fact table
the big downside is you have a much more complex schema with many more dimensions so only go for this if your dates are all frequently used.
In the example above, the user just wants to drill through and see all the dates so they can be left in the fact table in a Date Folder without their hierarchies
But this has been a really useful bit of research on marking the date table, Date Hierarchies and role playing
As ever with DAX, I tend to have to remind myself of the basic every so often, especially when i have bee concentrating on other topics.
We need to remember the following
Model Relationships propagate filters to other tables.
Product can be sold many times. (1 to many)
Have a look at the model in your Power BI desktop file
If you click on the join
You can see Cross Filter Direction (In this case Single) We can Filter the measure within the fact table by, for example, Product Name. But we cant Filter Product Name by, for example Sales amount within the fact table
When you are looking at Measures you basically filter a measure by either an implicit filter or an explicit filter within the DAX.
Confusing? How can the above information not be?
Lets take this a step backwards by Looking at implicit filtering
using the above example we have taken Color from the Product table and Order Quantity (The Metric) from the Fact table
We implicitly Filter Order Quantity by colour. No need to specify anything in DAX
Implicit – Suggested though not directly expressed
Lets create a measure
Order Quanity of Yellow Products = CALCULATE(SUM(FactInternetSales[OrderQuantity]),DimProduct[Color]=”Yellow”)
So here CALCULATE evaluates the summed value of Order Quantity, against the explicit filter of color = Yellow. So in the above visual, it ignores the implicit value of the Color filter within the visual.
Here is a nice reminder
If you drag a field into your visual its an implicit filter
If you set the filter within your DAX its an explicit filter and it will override what is in your visual
CALCULATE allows you to calculate a value against a context (The filter modification).
Lets change this slightly
Order Quantity of Yellow Products = CALCULATE(SUM(FactInternetSales[OrderQuantity]),ALL(DimProduct))
Now instead of Colour = “Yellow” We are saying Calculate against all Products
This time, note the total matches the total. this is because we are ignoring the colour context and Getting the total of ALL products
* quick sanity check. The visual isn’t quite right. The totals should be the same on the rows and the total column. This must simply be an issue with the visual I used here.
Filter basically returns a table that has been filtered. Lets have a look at a FILTER Function used in very much the Same way as CALCULATE above
TOTAL Order Quantity Yellow colour = CALCULATE(SUM(FactResellerSalesXL_CCI[Order Quantity]),FILTER(DimProduct,DimProduct[Color]="Yellow"))
We are again calculating the sum of Order Quantity, with a Filter of Color = yellow. Lets look at how the visual changes
This time, instead of seeing the total for yellow against every other colour quantity, we only as see the measure against yellow.
the great thing about FILTER is that you can have more than one Filter as an OR
TOTAL Order Quanity Yellow & Black = CALCULATE(SUM(FactResellerSalesXL_CCI[Order Quantity]),FILTER(DimProduct,DimProduct[Color]="Yellow"|| DimProduct[Color]="Black"))
Now we can see Yellow OR Black Quantities
how about if we want to see only yellow products in 2014. FILTER comes in useful for this
TOTAL Order Quanity Yellow & Black = CALCULATE(SUM(FactResellerSalesXL_CCI[Order Quantity]),FILTER(DimProduct,DimProduct[Color]="Yellow"),FILTER(DimDate,DimDate[CalendarYear] = 2014))
This time, Not only are we only seeing Yellow product Quantity but the Quantity sold in 2014
FILTER is obviously slower than CALCULATE so if you are only filtering on one thing, go for CALCULATE.
Bad Modelling 1: Single flat file table e.g. Salesextract
When people first start out using Power BI as their Analytics platform, there is a tendency to say, lets import all the data in one big flat file, like an Excel worksheet.
This way of working is just not well organised and doesn’t give you a friendly analytics structure.
Avoid Wide Tables
Narrow tables are much better to work with in Power BI. As the data volumes grows it will affect performance and bloat your model and become inefficient. then, when you create measures, things will start getting even more overly complex in the one long and wide table.
Not to mention the point when you have to add another table and create joins. You may be faced with the many to many join because of your wide table.
STAR SCHEMA are the recommended approach to modelling in Power BI
Stars with a few Snowflaked dimensions are also ok.
If you have a flat file wide table its always important to convert to an above data model with narrow dimension tables and a fact table in the middle with all your measures.
Remember, Chaos is a flat file.
Model Relationships propagate filters to other tables.
In this example the ProductID propagates down to the sales table. 1 Product can be sold many times. (1 to many)
With a snowflake you can add another level
CategoryA Propagates down to the Sales Fact table
Deliver the right number of tables with the right relationships in place.
Power BI was designed for the people who never had to think about the design of data warehouses. originally, this self service tool would allow any one with little or no knowledge of best practice to import data from their own sources, excel spreadsheets, databases etc without any knowledge of how they were set up.
This becomes an issue when the recommended Power BI model is the fact and dimension schemas as above.
Understanding OLAP models go a long way to helping you set up Power BI
Dimensions Filter and group
Facts Summarise measures
Bad Modelling 2: Direct Query your Transactional Database
When you connect up to OLTP and drag in all your tables ( there may be hundreds of them) using Direct Query there are lots of things to consider.
the overall performance depends on the underlying data source
When you have lots of users opening shared reports, lots of visuals are refreshed and queries are sent to the underlying source. This means that the source MUST handle these query loads for all your users AND maintain reasonable performance for those using the OLTP as they enter data.
You are not the most important person in this scenario. The person(s) using the database to add data is the most important person
OLTP is designed for speedy data input. OLAP is designed for speedy retrieval of data for analytics. These are to very different things.
With OLTP, you have row-Store indexes (Clustered Index, Non-Clustered Index) and these are slow for data analysis. They are perfect for OLTP style workloads. Data Warehouse queries, consume a huge amount of data, this is another reason why using OLTP as your direct query data source isn’t the best approach.
Also your Direct Query means you loose a fair amount of DAX functionality time time based DAX calculations, What if Parameters, etc.
I was chatting to someone about this on the forums and they gave me a fantastic analogy
When you connect into a transactional database with Direct Query, its like being in a busy restaurant and getting all the customers to go and get their food from the kitchen.
It slows down the customers because of the layout of the kitchen. They don’t know where anything is, and other customers are also milling around trying to find where their starter is.
the Kitchen staff who are now trying to prepare the food are having to fight for physical space. Look at the pastry chef, trying to work around 10 customers asking where their various desserts are?
So you set up a reporting area. This is where the food gets placed, someone shouts service and a waiter will go and speedily deliver the course to the correct table.
No one needs to go into the kitchen unless they are in food prep. Everything works in the most efficient way.
Model relationships Dos
Only 1 ID to One ID. If you have composite keys they need to be merged
No recursive Relationships (relationships that go back to the same table. the example always used for this is the managerID in the employer table
the Cardinality is 1 to many. 1 to 1. many to one. (Many to Many needs a specific approach in Power BI)
Cardinality determines whether it has filter group behavior or summarise behavior
There can only be one active path (relationship) Between two tables. All your other paths will be inactive (But you can set up DAX to use them)
In this example OrderDateKey is the active relationship because we use this the most and joins to DateKey
ShipdateKey and DueDateKey also join to DateKey in the date table and are inactive.
DAX Functions for Relationships to help with modelling decisions
When creating calculated columns you can only include fields from the same table. Unless you use RELATED
For example, I’m adding the column Colour into the SalesOrderDetail table which has a Many to One join to Products •Colour = RELATED(Products[Colour])
RELATED allows you to use data from the one side in the many side of the join
RELATEDTABLE Uses data from the Many side of the Join
Modifies the filter direction Disables propagation. You can actually do this in the model by changing the filter to both directions instead of single. OR you can do it for a specific DAX query using CROSSFILTER
Our Unconnected Budgeted Data is in Year only and its not joined to our main model.
Here we connect up to Year in Date. then we can create a visal with Date from the Date dimension. Total sales from our connected data which is at daily level and Total Budget from our unconnected budgeted data at a different level of granularity.
Naturalise a recursive relationship with the PATH function
Getting your model right and understanding your data sources is the most important thing to get right with Power BI. make sure you don’t have lots of headaches six months into your project. Its better to spend the time now, than having to start again later.
I have gone through a fair few training courses on DAX now because its an important part of Microsoft Analytics. I thought It would be nice to include all my notes from one of the first DAX courses I attempted.
You don’t have to be an expert on DAX to get started with Power BI. You can start with a few of the basics and get lots of help along the way in the forums.
DAX (Data Analysis Expressions) is an expression language for slicing and dicing analytical data
Where is DAX Used?
Power Pivot (Excel)
SSAS Tabular Mode (You can’t use it in Multidimensional mode)
Azure Analysis Services (This is only available in Tabular Mode)
DAX IS USED HEAVILY IN THE MICROSOFT BI STACK
Where Does DAX Shine?
Aggregations and filtering. Its optimized for both
What you need
An easy way of defining key metrics.
You need to be able to slice and dice
You need to be able to do historical analysis
DAX is an easy way of defining key metrics.
What is DAX not good at?
Operational Reporting – Detail heavy used for day to day operating. Line by Line Reports
Wide tables – Tables with a lot of columns
Many to Many relationships. There are ways around this, but it can be difficult to resolve
Its worth noting that this visual was provided over a year ago when Azure Analysis Services was the only way of creating the back end centralised model. we are now at December 2020 and Power BI Has moved on to become not only Self Service, but a really great way to implement a Standard centralised model for Enterprise reporting. You do this by creating data flows in Service, which establishes your transformations in one specific area for reuse. Then over this, data sets can be created that can be reused by other developers once you have promoted them.
Thinking in columns not rows
OLTP – Online Transactional Processing. (Normalised schemas for frequent updates)
OLAP – Online analytical Processing (Fact and Dimensions. Star Schemas etc.)
Single column aggregations – Sales by area etc. (OLAP)
Large number of rows – Sales by year, we have 10 years of data. Lots of rows (OLAP)
Repeated values – Data is flattened unlike in an OLTP
Need to quickly apply filters By Area, Postcode, Year etc.
We may only want 3 columns in a table that has 50 columns. We just want the slice of those 3 columns and we don’t want to read the other columns
For this we store data as columns Not Rows
Also known as xVelocity. It is the engine used to store data as columns. The data is imported into Power BI data center as Columns not rows
If you set up your connection as a direct Query, Power BI has to translates DAX formulas into relational SQL queries so you lose a lot of the functionality like Time DAX because its too complex for SQL.
Compression and Encoding
This is how Power BI Compresses your data. Each column is compressed separately
Let’s take the lowest value in the range
and then store everything else as the delta (Difference) of that value C.
This makes the Code shorter in length, compressing the data
The value gets assigned a number which is then used in place of the actual data item
This takes up far less space.
The data is sorted
This just keeps the colour and the number of repeats. Repeating values creates excellent compression. Unique values, not so much.
Adding Business Logic with Calculated Columns and Measures
The following examples have been set up using the old faithful Adventureworks data base.
Im initially bringing through two tables
and renaming them to Products and SalesOrderDetail
We are now ready to try some examples
Where should you be creating calculated columns? In Power Query using M Language or in DAX.
the speedy answer is, if you can, always create them in Power Query. However, you do need to understand how the calculated column works in DAX in order to understand measures
Expands a table by adding a new column.
Operational, Detailed information. Can only look at the specific row
It’s an expression that produces a column. Computes at the time of data refresh and is stored within the table
Limited by a row context. Price-Discount. They don’t take advantage of the columnar database
In Power BI we are going to set up a Line total in SalesOrderDetail because you need where possible to put the new column in the right table with the data that is being used to create it
Click on … Against the table under fields in power BI and New Column
The new column now sits in the model with the other fields (Go to Data Tab)
And you can use this like any other metric. In this table we are filtering by product Colour. Line Total has already been calculated within the row context.
You can now use Line Total in a table visualization because we can treat this column like any other column and its now being set in the implicit filter context which in this case is Color.
Implicit context filters are when you add a description column which aggregates your metric within the visual. Or if you add a filter to the visual. We will look at Explicit filters later.
When you create a column you can only create it from data in the same table unless you add RELATED or RELATEDTABLE into your DAX
Adding Color into the SalesOrderDetailTable from Products
1 Product can be sold Many times.
Colour = RELATED(Products[Color])
I have added data from another table into a table. RELATED allows you to pull data across from another related table. Note that in the previous DAX I only used data from one table, so I didn’t need to use RELATED.
RELATED is for the One to Many Relationship. Using data from the one side in the many side. Colour (from 1) now sits in salesOrderDetail (M)
RELATEDTABLE uses the data from the many in the one side
The SUMX is an Iterator. Takes a table and an expression to evaluate. This means We are going through each row in the Products table and its running the evaluation. It’s using the related table to go through all of the LineTotal’s that we created in SalesOrderDetail
So for example
Row for Product ID 707. Sum up the Line total in salesOrder Detail where ProductID 707 and add the line total into Product
Next iteration. Row for ProductID 708. Sum up the Line total in salesOrder Detail where ProductID 708 and add the line total into Product
And repeat until you have iterated through the entire table for each row
Again, a quick rule of thumb is, if you are creating a calculated column using data from the same table, do it in Power Query Editor. If you have to use data from other tables, use DAX.
Your data will be compressed like any other field if its been created with Power Query Editor but it wont be if its a calculated column because it happens after compression.
Summarises all the data into a single value. Not stored on the table.
Analytical. Takes a column and brings back a summary
They are computed at runtime so stored temporarily
Every time you open a report, your Measures are computed
Limited by a filter context (Rather than a row context)
A measure looks at the data minus what has been filtered out by the user at that time.
They are more loosely associated with a table, so you don’t need to RELATE tables
Again, In Power BI on the SalesOrderDetail Table: Create Measure
Minimum Price = Min(SalesOrderDetail[UnitPrice])
You can’t add your measure to a slicer or use as a filter because its created after the filters have been set
Implicit Measure – Underneath the hood is a measure for anything that you aggregate that is created by the DAX engine. For example your Total column. Here we are implicitly filtering UnitPrice by Colour to get the minimum value.
If you go into the Data tab, you wont see this measure because it only exists after you create your visual.
Filter data Using Calculate
Applied by the user or the layout of the report. The visuals implicitly filter the data. When you drill up and down on a visual for example.
Coded into the DAX Expression. Explicit filtering overrides Implicit filtering
Calculate changes the current evaluation context
In Power BI set up a Table containing Products Colour and Unit Price (Set to Average rather than Sum)
So for Full Finger Gloves L.44 were bought, Around 17 dollars each with a discount of 15%
the Average of UnitPriceDiscount is the same as the Summed UnitPriceDiscount because the products are all identical with the same discount applied
44 $17 gloves would bring in $752. Applying the discount of 15% (0.15) shows is that £112.83 has been discounted from the total price.
This is above 10 so we can simply display the average Unit Price
Historical Sales = CALCULATE (SUM ([Total]), ALL (‘Date’) )
ALL clears any filters in the entire date table
For this example, we want the Sum of Order Quantity for the specific context filter divided by (We now need calculate because we are manipulating filters) Sum of all Order Quantities.
ALL takes in just the product table because we want to undo any filters from the Product table (New Measure in the Products Table)
% of total sales = SUM(SalesOrderDetail[OrderQty]) / CALCULATE(SUM(SalesOrderDetail[OrderQty]), ALL(Products))
So for Black context filter the Order Quantity is 81937 / the total (We have removed the expression filter for the entire product table) of 274914 so we can see that Black is 29.80% or the order total.
With a slicer on the report. We choose One Product and even though its the only row in the visual Total Sales shows -.13% instead of 100% which is just what we want.
We still have 18% of Total Sales instead of it showing 100% because that’s the only row left in the visual. Perfect. This is what would have happened without ALL
% of total sales = SUM(SalesOrderDetail[OrderQty]) / CALCULATE(SUM(SalesOrderDetail[OrderQty]))
Looping over the Data with Iterators
Allows you to use multiple columns in an aggregation
What is an iterator?
Power BI’s DAX engine is optimized for working with columns not rows.
Iterators can process on a row by row manner. Its less performant because its working with rows.
Takes in a table parameter (What is it looping through)
Then takes in an expression (For each row, evaluate this expression)
We have used something before that takes in the table and then an expression. The Filter function. The Filter function is an iterator.
Many of them end in X. SUMX MAXX CONCTENATEX etc
Average Gross Sales =
AVERAGEX(Category, [Quantity] * [Price] )
You could create Quantity* Price as a calculated column so each row gets this valuated first, and then average this column separately. The iterator does both in one formula
Add a new Measure into SalesOrderDetail and start typing in the following (Type it in so you bring up the intellisense)
AverageGrossSales = AVERAGE(SalesOrderDetail[OrderQty] * Uni
If you type in the above you notice intellisense stops working when you get to Unit price. This doesn’t work. The average function only accepts a single column.
This is where you could create this part as a calculated column but we want everything in one measure
Its only called Incorrect because this is the wrong way to do it
This measure should show us what colours we have filtered on but as you can see below, now I have added a Card. We get the filtered colours for every row and we don’t want that. The Concatenate is iterating through every row and adding every colour together