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Medium Power BI Interview Questions

95 medium questions with answers. Applied questions that check whether you can use the concepts on real work.

Topics in the medium set

Visualisation and Report Design: 15 DAX Fundamentals: 13 Power Query and Data Transformation: 12 Power BI Service, Sharing and Security: 12 Data Modelling: 11 Advanced DAX and Time Intelligence: 11 Performance Optimisation and Administration: 11 Power BI Fundamentals: 10
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01

What are Import, DirectQuery and Live Connection modes?

Power BI FundamentalsMedium
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Import loads a compressed copy of data into the in-memory VertiPaq engine, giving the fastest queries but requiring refresh. DirectQuery sends queries to the source at view time, so data is current but performance depends on the source and some DAX is limited. Live Connection connects a report to an existing semantic model or Analysis Services model without its own model. Composite models mix Import and DirectQuery tables.
02

What licence types exist for Power BI?

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Power BI Free lets a user build in Desktop and use My workspace but not share content. Power BI Pro is needed to publish to shared workspaces and share with other Pro users. Premium Per User adds larger models, more refreshes and premium features per user. Fabric capacity (F SKUs) provides dedicated capacity; at F64 and above, viewers with a free licence can consume shared content.
03

What is the relationship between Power BI and Microsoft Fabric?

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Microsoft Fabric is Microsoft's unified analytics platform that includes data engineering, data factory, data warehousing, real-time analytics and Power BI as its reporting layer. Power BI workspaces can live on Fabric capacity and use items such as lakehouses and warehouses in OneLake. Direct Lake mode lets semantic models read Delta tables in OneLake directly without a full import, combining fresh data with near-import speed.
04

What are paginated reports and when would you use them?

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Paginated reports, built with Power BI Report Builder, are pixel-perfect, print-ready reports that can span many pages, such as invoices, statements or regulatory reports with long tables. They are ideal when users need exact layout, export to PDF or Excel, or detailed row-level listings. Interactive Power BI reports are better for exploration. Paginated reports can run in the Service with Pro, PPU or Fabric capacity.
05

Users say the report shows yesterday's data even after a refresh. How do you troubleshoot?

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I would check the refresh history in the Service for errors or whether the refresh actually ran, confirm the gateway is online and has valid credentials, and verify the source itself has the latest data. Then check for cached dashboard tiles, query caching, or an incremental refresh policy that excludes recent days. Also confirm users are viewing the right workspace or app version, which may need republishing.
06

Your organisation has 500 report viewers. How would you plan licensing?

Power BI FundamentalsMedium
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Giving all 500 viewers Pro licences is one option. If there are many viewers and heavy models, Fabric capacity at F64 or above lets free-licence users view content in workspaces on that capacity, while report creators still need Pro or PPU. I would compare costs, workload size and features like larger models with IT, and recommend the option that fits usage, without assuming one choice fits all.
07

Tell me about a report you built that changed a business decision.

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Situation: regional managers tracked sales in separate Excel files, and stock planning was late. Task: give one daily view. Action: I combined ERP and target data in Power Query, built a star schema with DAX measures for target achievement and stock cover, and published an app with row-level security per region. Result: weekly planning moved from Friday to Monday morning, and two slow-moving products were discontinued earlier.
08

What is query folding and why does it matter?

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Query folding is when Power Query translates transformation steps into a native source query, such as SQL, so the source does the work and only the result is loaded. It makes refreshes much faster and is required for incremental refresh and efficient DirectQuery. Steps like filtering, removing columns and grouping usually fold on SQL sources, while some custom M functions or adding an index column can break folding.
09

What are query parameters in Power Query?

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Parameters are named values used inside queries, such as server name, database, file path or a date range. They let you switch from a development to a production database without editing each query, and they are required for incremental refresh through RangeStart and RangeEnd. Parameters can be changed in the Service under semantic model settings, which helps deployment pipelines between environments.
10

What is a dataflow and how is it different from Power Query in Desktop?

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A dataflow runs Power Query transformations in the Power BI Service and stores the result in the cloud, so multiple semantic models can reuse the same cleaned tables. Desktop Power Query logic lives inside one model only. Dataflows Gen2 in Fabric can also write output to lakehouses or warehouses. Dataflows centralise preparation logic, reduce duplicate source load and separate data prep from modelling.
11

What is the difference between Reference and Duplicate in Power Query?

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Duplicate copies all the steps of a query into a new independent query, so later changes to the original do not affect it. Reference creates a new query whose source is the output of the original, so it inherits any changes. Reference is useful for building several tables from one staging query, such as dimension tables from a cleaned sales table, while Duplicate is for experimenting separately.
12

Refresh takes 90 minutes because of heavy Power Query steps. How do you speed it up?

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I would check query folding with View Native Query or the folding indicators and move non-folding steps after folding ones. Filter rows and remove unused columns as early as possible, push joins and aggregations into SQL views, avoid row-by-row custom functions over large tables, and disable load for staging queries. For large fact tables, set up incremental refresh so only recent partitions reload.
13

Sales data has region codes, while targets use region names. How do you combine them?

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I would create or import a region mapping table with code and name, clean both sides by trimming spaces and fixing case, then merge in Power Query or better, build a Region dimension table with both columns and relate sales by code and targets by name to it. Unmatched rows should be checked using a left anti join so missing mappings are fixed rather than silently dropped.
14

A source table has duplicate customer rows with different spellings of the same name. What do you do?

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For exact duplicates, Remove Duplicates on the key column. For spelling variations, use fuzzy matching in Merge Queries with a similarity threshold and transformation table, review results, and maintain a mapping table of approved matches. The best long-term fix is to use a stable customer ID from the source system and report data quality issues to the owner rather than cleaning endlessly in Power BI.
15

Write an M query that filters rows, removes columns and changes types.

Power Query and Data TransformationMedium
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let Source = Sql.Database("server", "SalesDB"), Orders = Source{[Schema="dbo", Item="Orders"]}[Data], Filtered = Table.SelectRows(Orders, each [OrderDate] >= #date(2024, 1, 1)), Kept = Table.SelectColumns(Filtered, {"OrderID", "OrderDate", "CustomerID", "Amount"}), Typed = Table.TransformColumnTypes(Kept, {{"Amount", Currency.Type}, {"OrderDate", type date}}) in Typed All these steps fold to SQL on a database source.
16

Create a date table in Power Query using M.

Power Query and Data TransformationMedium
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let StartDate = #date(2022, 1, 1), EndDate = #date(2026, 12, 31), Days = Duration.Days(EndDate - StartDate) + 1, Dates = List.Dates(StartDate, Days, #duration(1, 0, 0, 0)), T = Table.FromList(Dates, Splitter.SplitByNothing(), {"Date"}), Typed = Table.TransformColumnTypes(T, {{"Date", type date}}), Y = Table.AddColumn(Typed, "Year", each Date.Year([Date]), Int64.Type), M = Table.AddColumn(Y, "Month", each Date.MonthName([Date]), type text) in M
17

Describe a time you cleaned very messy data under a deadline.

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Situation: a client sent 36 monthly Excel files with merged headers and changing columns two days before a review. Task: build a consolidated sales report. Action: I used the Folder connector with a custom function that promoted the right header row, unpivoted month columns and mapped renamed fields through a lookup table. Result: the report was ready a day early, and future files loaded automatically with no manual work.
18

What is cross-filter direction and why is bi-directional filtering risky?

Data ModellingMedium
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Cross-filter direction controls which way filters travel across a relationship. Single direction, from the one side to the many side, is the default and safest. Bi-directional lets the fact table filter the dimension too, which can be useful for slicers showing only relevant values, but it can cause ambiguous paths, unexpected results and slower queries. Prefer single direction and use CROSSFILTER inside specific measures when needed.
19

What are active and inactive relationships?

Data ModellingMedium
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Only one active relationship can exist between two tables along a filter path; additional relationships become inactive and appear as dashed lines. For example, Sales may have OrderDate and ShipDate both linked to Date, with OrderDate active. An inactive relationship is used only inside a measure with USERELATIONSHIP, such as CALCULATE([Sales], USERELATIONSHIP(Sales[ShipDate], 'Date'[Date])).
20

What is a role-playing dimension and how do you handle it?

Data ModellingMedium
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A role-playing dimension is one dimension used in several roles, such as Date acting as Order Date, Ship Date and Delivery Date. Options are one Date table with one active and other inactive relationships used through USERELATIONSHIP in measures, or separate copies of the date table for each role so users can slice by each date independently. The second is easier for users but increases model size slightly.
21

What is a snowflake schema and should you avoid it in Power BI?

Data ModellingMedium
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A snowflake schema normalises dimensions into several related tables, such as Product linked to Subcategory linked to Category. It saves little space in Power BI because columnar compression already handles repetition, and it adds relationships, longer filter paths and a more confusing field list. Usually it is better to flatten these into one Product dimension in Power Query, keeping the model a clean star.
22

What is a calculated table and when would you use one?

Data ModellingMedium
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A calculated table is created with a DAX expression and stored in the model, recalculated at refresh. Examples are a date table using CALENDAR, a disconnected parameter table for what-if analysis, or a summary table. It is handy but adds memory, and it cannot use Power Query folding. For most shaping tasks, creating tables in the source or Power Query is preferred.
23

Your model has one wide flat table with 80 columns from an Excel export. How would you remodel it?

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I would identify the grain, such as one row per order line, and split descriptive attributes into dimension tables like Customer, Product, Store and Date using Reference queries and Remove Duplicates on keys. The fact table keeps keys and numeric columns only. Then create one-to-many single-direction relationships. This reduces size, simplifies DAX and makes slicers faster and more reliable.
24

A slicer on Product Category does not filter the Targets visual. What do you check?

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I would check the relationship path in model view: whether Targets is related to the Product or Category dimension at all, whether the relationship is active, and its cross-filter direction. If Targets are at category level, it needs a relationship to a Category table that also filters Product. Also check whether visual interactions were turned off for that slicer and whether the measure uses ALL or REMOVEFILTERS.
25

Users want to analyse sales by both order date and delivery date in the same report. What do you do?

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I would keep the Date table related to OrderDate as the active relationship and add an inactive relationship to DeliveryDate. Then create measures like Sales by Delivery Date using USERELATIONSHIP. If users need separate slicers for both dates at the same time, I would create a second Delivery Date table as a role-playing copy related actively to the delivery column.
26

How do you create a fiscal year column starting in April?

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Fiscal Year = VAR m = MONTH('Date'[Date]) VAR y = YEAR('Date'[Date]) RETURN "FY " & IF(m >= 4, y, y - 1) & "-" & RIGHT(IF(m >= 4, y + 1, y), 2) For April 2026 this returns FY 2026-27, which matches the Indian financial year. Add a fiscal month number column for sorting too.
27

Tell me about a time you redesigned a data model.

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Situation: a finance report took 40 seconds per page with a 2 GB file built on joined flat tables. Task: improve speed. Action: I split it into a star schema with Date, Account, Cost Centre and fact tables, removed unused columns, turned off auto date/time and replaced bi-directional filters with single direction. Result: model size dropped to 450 MB and pages loaded in under 4 seconds.
28

What is the grain of a fact table and why does it matter?

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Grain is the level of detail of one fact row, such as one row per order line per day. It must be defined clearly before building measures, because mixing grains in one table, for example daily sales and monthly targets, causes double counting and wrong totals. Facts at different grains should be separate tables related to dimensions at the matching level.
29

Explain row context and filter context.

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Row context means DAX is evaluating one row at a time, which happens in calculated columns and iterators like SUMX, so you can refer to column values of the current row. Filter context is the set of filters applied to the model from slicers, visual rows, columns and CALCULATE. Measures are evaluated in filter context. Row context does not filter the model unless converted by context transition.
30

What does CALCULATE do?

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CALCULATE evaluates an expression in a modified filter context. Its filter arguments can add, replace or remove filters, for example CALCULATE([Total Sales], 'Product'[Category] = "Electronics") replaces any category filter with Electronics. It also performs context transition when used inside a row context, turning the current row into an equivalent filter. It is the most important function in DAX.
31

What is the difference between ALL, ALLEXCEPT and REMOVEFILTERS?

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ALL returns all rows of a table or column ignoring filters, and as a CALCULATE argument it removes filters, useful for percent of total. REMOVEFILTERS does the same removal but only as a CALCULATE modifier and reads more clearly. ALLEXCEPT removes all filters from a table except the listed columns, such as keeping the Year filter while removing others. ALLSELECTED keeps filters from outside the visual, like slicers.
32

What are variables in DAX and why use them?

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VAR defines a named value inside an expression and RETURN gives the final result. Variables make measures easier to read, avoid repeating the same calculation, which improves performance, and help debugging because you can return an intermediate variable. A variable is evaluated once in the context where it is defined, so its value does not change if later CALCULATE filters are applied.
33

A measure shows the same value on every row of a table visual. Why?

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The measure is probably ignoring the filter context of the rows, for example using ALL on that column or table, or the row field comes from a table that is not related to the fact table, so its filter cannot reach the data. I would check relationships in model view, the direction of filtering, and any ALL or REMOVEFILTERS in the measure.
34

The total row of a table shows a different value than the sum of rows. Is this a bug?

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Usually not. A measure's total is calculated in the total's own filter context, not by adding the visible rows. For non-additive measures like averages, distinct counts or ratios this differs from the row sum. If business wants the sum of rows, I write it explicitly with SUMX over the row values, for example SUMX(VALUES('Product'[Product]), [My Measure]).
35

Your calculated columns have made the model huge. What do you do?

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I would move simple row-level logic into Power Query or the source SQL, where it compresses better and can fold, and replace aggregations stored as columns with measures. High-cardinality columns such as concatenated keys or precise timestamps should be removed or split. Then check model size with VertiPaq Analyzer in DAX Studio to confirm which columns used the most memory.
36

Write a measure for percentage of grand total sales.

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Sales % of Total = DIVIDE( [Total Sales], CALCULATE([Total Sales], REMOVEFILTERS('Product')) ) This gives each product's share of total across all products. Use ALLSELECTED('Product') instead if the denominator should respect slicer selections on products.
37

Create a calculated column that categorises customers by their lifetime sales.

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Customer Band = VAR s = CALCULATE(SUM(Sales[Amount])) RETURN SWITCH(TRUE(), s >= 500000, "Platinum", s >= 100000, "Gold", s > 0, "Silver", "No Purchase") This is a column on the Customer table; CALCULATE triggers context transition so each row gets its own customer's sales.
38

Write a measure that counts customers with sales above 10,000.

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Big Customers = COUNTROWS( FILTER( VALUES(Customer[CustomerID]), [Total Sales] > 10000 ) ) Iterating VALUES of the customer key keeps the loop small and respects current filters such as year or region.
39

Tell me about a time you found a wrong number in a published report.

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Situation: a regional head noticed our margin report did not match finance. Task: find and fix it quickly. Action: I compared numbers at product level, found returns were double-subtracted because a measure used both a net amount column and a returns table. I fixed the measure, added a reconciliation page against finance totals and informed users. Result: numbers matched to the rupee and the reconciliation check became standard.
40

What is the difference between SAMEPERIODLASTYEAR, DATEADD and PARALLELPERIOD?

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SAMEPERIODLASTYEAR shifts the current dates back exactly one year. DATEADD shifts by any number of days, months, quarters or years, such as DATEADD('Date'[Date], -1, MONTH) for last month. PARALLELPERIOD also shifts by an interval but returns the full shifted period, for example the whole previous quarter even if only one month is selected. Choose based on whether partial periods should be compared.
41

How do you handle a fiscal year in time intelligence functions?

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Functions like TOTALYTD and DATESYTD accept a year-end date argument, so for an Indian fiscal year ending 31 March use TOTALYTD([Sales], 'Date'[Date], "31/3"). Add fiscal year, quarter and month columns to the date table for slicing. For complex calendars such as 4-4-5 retail weeks, standard functions do not work, and you write custom logic using fiscal period columns. Newer calendar-based time intelligence also supports custom calendars.
42

What are field parameters in Power BI?

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Field parameters let report users switch which measure or dimension a visual shows using a slicer, for example choosing between Sales, Profit and Units, or switching the axis between Region and Category. They are created through Modeling, New parameter, Fields, which generates a calculated table. They reduce the number of duplicate visuals and bookmarks needed for dynamic reports.
43

What are the most useful table functions in DAX?

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Key table functions include FILTER, ALL, VALUES, DISTINCT, SUMMARIZE and SUMMARIZECOLUMNS for grouping, ADDCOLUMNS to add calculated columns, TOPN for top rows, CROSSJOIN, UNION, EXCEPT, INTERSECT, GENERATESERIES and TREATAS for virtual relationships. They return tables used inside iterators, CALCULATE filters or calculated tables. ADDCOLUMNS over SUMMARIZE is a common pattern for reliable grouped results.
44

Explain how RANKX works and common mistakes with it.

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RANKX iterates a table, evaluates an expression for each row and ranks the current value among them. A common pattern is RANKX(ALL('Product'[Product]), [Total Sales]). Mistakes include not using ALL, so every product ranks 1 because only one is visible, ranking over a table with duplicates, and forgetting ties handling with the Dense option. The newer RANK function supports multi-column ordering.
45

What are visual calculations?

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Visual calculations are DAX calculations defined directly on a visual and computed on the visual's own aggregated data, rather than on the model. They make running totals, moving averages, percent of parent and comparison with previous rows simpler using functions like RUNNINGSUM, MOVINGAVERAGE and PREVIOUS. They do not add measures to the model, so they suit visual-specific logic but cannot be reused across visuals.
46

What is a disconnected table and how is it used for what-if analysis?

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A disconnected table has no relationship to the model and is used to capture a user's choice through a slicer. For example, a Discount table from 0 to 30 percent created with GENERATESERIES, or the What-if parameter feature, lets a measure read SELECTEDVALUE(Discount[Value]) and calculate projected revenue. Since it does not filter facts, the measure decides how the selection is applied.
47

Business wants year-over-year growth, but the current year is incomplete. How do you compare fairly?

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Comparing a partial year with a full last year understates growth. I would limit last year to the same date range, for example using the last date with sales this year and filtering last year's dates up to the matching day, or compare year-to-date to previous year-to-date. I would label the visual clearly as YTD versus same period last year so readers understand it.
48

A YTD measure returns blank for future months on a chart. Users want the line to stop at today. How?

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The issue is the opposite for many teams: YTD repeats the last value for future months. I would add a condition so the measure returns BLANK when the period starts after the last date with data, for example IF(MIN('Date'[Date]) > [Last Sales Date], BLANK(), TOTALYTD(...)). Alternatively add a column flagging dates up to today in the date table and filter the visual on it.
49

Write a running total measure.

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Running Total = VAR maxDate = MAX('Date'[Date]) RETURN CALCULATE( [Total Sales], 'Date'[Date] <= maxDate, REMOVEFILTERS('Date') ) REMOVEFILTERS clears the current period filter so all earlier dates are included. In a visual-only scenario, the visual calculation RUNNINGSUM is simpler.
50

Write a dynamic rank measure for products.

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Product Rank = IF( ISINSCOPE('Product'[Product]), RANKX(ALLSELECTED('Product'[Product]), [Total Sales], , DESC, DENSE) ) ALLSELECTED ranks within the products visible after slicers, and ISINSCOPE hides the rank on total rows.
51

What are bookmarks and how are they used?

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Bookmarks capture the current state of a report page, including filters, slicers, visual visibility and sort order. They are used for storytelling, toggling between chart and table views with buttons, creating custom navigation, and resetting filters. Combined with the selection pane, they show and hide visuals. Too many bookmarks become hard to maintain, so field parameters are often a simpler alternative for switching measures.
52

What are tooltips and report page tooltips?

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Default tooltips show field values when hovering over a data point. Report page tooltips let you design a small custom page, set as a tooltip page type, showing extra visuals like a mini trend chart for the hovered category. They add detail without cluttering the main page. Keep tooltip pages light because they run queries on every hover.
53

How do you control how visuals interact with each other?

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By default, selecting a data point cross-filters or cross-highlights other visuals on the page. Use Format, Edit interactions to choose filter, highlight or none for each visual pair, for example stopping a slicer from affecting a target KPI card. Slicers can also be synced across pages with the Sync slicers pane. Clear interaction design prevents confusing behaviour.
54

How do you design reports for accessibility?

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Use sufficient colour contrast and do not rely on colour alone, for example add icons or labels to red and green. Set alt text on visuals, a logical tab order in the selection pane, clear titles and readable font sizes. Avoid tiny text and very dense pages. Power BI supports screen readers and keyboard navigation, and high-contrast themes help users with low vision.
55

When would you use a custom visual and what are the risks?

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Custom visuals from AppSource add chart types not built in, such as Gantt charts, sankey diagrams or advanced KPI cards. Risks include performance issues, limited support, export and accessibility gaps, and data security, since some visuals may call external services. Prefer certified visuals, check organisational policy, since admins can restrict them, and use built-in visuals where they meet the need.
56

Users complain the report page is cluttered with 22 visuals. How do you redesign it?

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I would ask which decisions the page supports and keep only visuals that answer those questions. Then group related KPIs into a top row of cards, keep two or three main charts, and move details to drill-through or tooltip pages. Slicers can move into a collapsible panel using bookmarks. Fewer visuals also make the page load faster.
57

A stakeholder insists on a 3D pie chart with 12 slices. How do you handle it?

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I would understand what they want to see, usually share of total by category, then show a quick comparison: a sorted bar chart beside the pie, explaining that bars make small differences readable while 3D distorts sizes. Offering a donut with top five plus Others is a compromise. Usually seeing both side by side convinces them, and the final choice remains theirs.
58

Executives want a one-page story of quarterly performance. How do you structure it?

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I would start with three to five headline KPIs versus target and last year at the top, then a trend chart showing the quarter's movement, then a breakdown by region or product showing what drove the change, and finally a short text box or smart narrative stating key takeaways and actions. Each element answers the next natural question, and details live on drill-through pages.
59

How do you create a measure-driven conditional colour?

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Sales Colour = VAR ach = DIVIDE([Total Sales], [Target]) RETURN SWITCH(TRUE(), ach < 0.9, "#D64550", ach < 1, "#F2A93B", "#2E9E5B") In the visual, open conditional formatting for background or font colour, choose Format style Field value and select this measure.
60

How do you build a toggle between a chart and a table using bookmarks?

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Place a chart and a table in the same position. In the Selection pane hide the table and create a bookmark named Chart View with Data unchecked so filters are not saved; then show the table, hide the chart and create Table View. Add two buttons and set each button's action to the matching bookmark. Group the visuals to keep the layout tidy.
61

How do you create a dynamic axis using field parameters?

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Go to Modeling, New parameter, Fields, and add the fields such as Region, Category and Channel. Power BI creates a parameter table and slicer. Put the parameter field on the axis of a chart; users select which dimension to show from the slicer. You can add measures to a separate field parameter so users switch both the measure and the axis.
62

How do you build a custom tooltip page?

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Create a new page, set Page information, Allow use as tooltip on, and set Canvas settings to the Tooltip size. Add small visuals like a monthly trend line for the hovered item. On the main visual, go to Format, Tooltips, set Type to Report page and select the tooltip page. Fields in the main visual automatically filter the tooltip page on hover.
63

Tell me about a time a user rejected your report design. What did you do?

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Situation: sales managers stopped using a dashboard I built. Task: find out why. Action: I watched two managers use it and found they needed weekly target gaps first, which were hidden on page three. I moved those to the top, removed four rarely used charts and added drill-through for details. Result: weekly usage in the activity log tripled within a month.
64

What is the difference between SELECTEDVALUE and VALUES?

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SELECTEDVALUE(column, alternate) returns the single value of a column when exactly one is visible in the filter context, otherwise the alternate or blank. VALUES(column) returns a table of distinct visible values, including blank for unmatched rows, and can be used in iterators or as a filter. Use SELECTEDVALUE for titles and parameters, and VALUES when you need to loop over the visible items.
65

Your measure returns an error that a table of multiple values was supplied where a single value was expected. How do you fix it?

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This happens when an expression like VALUES or a column reference returns several rows where a scalar is needed, for example in IF or comparison. I would use SELECTEDVALUE with a fallback, wrap the column in an aggregation like MAX or SUM, or use HASONEVALUE to check first. If iteration is needed, use SUMX or another iterator over VALUES instead.
66

What is the difference between static and dynamic RLS?

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Static RLS hard-codes values in each role, such as one role per region, which becomes hard to manage as regions grow. Dynamic RLS uses one role with a filter based on the logged-in user, such as Users[Email] = USERPRINCIPALNAME(), with a security mapping table linking users to the regions or managers they may see. Dynamic RLS scales better and is driven by data rather than role edits.
67

What is the difference between sharing a report, publishing an app and using a workspace?

Power BI Service, Sharing and SecurityMedium
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A workspace is where creators collaborate. Direct sharing gives one person or group access to a single report, which is quick but hard to govern at scale. An app packages reports and dashboards from a workspace for consumers, with audiences controlling who sees which content, and updates only when republished. Apps are the recommended way to distribute content to large business audiences.
68

What are deployment pipelines?

Power BI Service, Sharing and SecurityMedium
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Deployment pipelines move content through stages, typically Development, Test and Production workspaces. Creators deploy reports and semantic models from one stage to the next, compare differences, and use deployment rules to change data source connections or parameters for each stage. This supports controlled releases and testing before users see changes. They work alongside Git integration for version control in Fabric workspaces.
69

What is incremental refresh?

Power BI Service, Sharing and SecurityMedium
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Incremental refresh partitions a large table by date so each refresh reloads only recent data, such as the last 10 days, while keeping older partitions, such as five years of history, unchanged. It uses the RangeStart and RangeEnd datetime parameters to filter the query, which must fold to the source. It cuts refresh time and load on sources, and can add a DirectQuery partition for real-time data.
70

What are endorsement, sensitivity labels and lineage view?

Power BI Service, Sharing and SecurityMedium
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Endorsement marks content as Promoted by its owners or Certified by authorised reviewers, guiding users to trusted semantic models. Sensitivity labels from Microsoft Purview classify content, such as Confidential, and labels flow to exports like Excel and PDF. Lineage view shows how data sources, dataflows, semantic models, reports and dashboards depend on each other, which helps impact analysis before changes.
71

Each regional manager must see only their region, and the CEO must see everything. How do you implement this?

Power BI Service, Sharing and SecurityMedium
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I would build dynamic RLS with a security table of Email and Region, related to the Region dimension, and a role filter Security[Email] = USERPRINCIPALNAME(). The CEO and other full-access users get an 'All' flag handled in the rule, or are placed in a separate role with no filter. I would test with View as role in Desktop and in the Service before publishing the app.
72

Scheduled refresh fails every night with a gateway error. How do you troubleshoot?

Power BI Service, Sharing and SecurityMedium
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I would check the refresh history error details, confirm the gateway machine is on and the gateway service is running and updated, and verify data source credentials in the gateway connection have not expired. Then test connectivity from the gateway machine to the source and check that the source names in the model exactly match the gateway data source. Gateway logs and network or firewall changes are next.
73

Business users keep asking for edits directly in production reports. How do you set up a better process?

Power BI Service, Sharing and SecurityMedium
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I would set up separate Development, Test and Production workspaces with a deployment pipeline, store PBIP files in Git, and route requests through a simple backlog. Changes are built in Dev, reviewed by a key user in Test and deployed to Production on a release schedule. Users consume through an app, so production stays stable and changes are traceable.
74

Tell me about a time you handled a data access or security issue.

Power BI Service, Sharing and SecurityMedium
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Situation: a sales user reported seeing another region's numbers after a reorganisation. Task: fix the leak fast. Action: I confirmed the security mapping table had stale entries, removed the user from the wrong row, refreshed the model and then automated the mapping from the HR system with a daily refresh. I informed the data owner. Result: access stayed correct after later reorganisations, and quarterly access reviews were added.
75

How do you mentor junior Power BI developers in your team?

Power BI Service, Sharing and SecurityMedium
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I pair with them on real tasks, review their models and DAX with clear reasons rather than just fixes, and share a short checklist covering star schema, naming, measures over columns and performance checks. I give them ownership of small reports early. One junior I mentored moved from building single-table reports to owning a shared finance model within six months.
76

How does the VertiPaq engine store and compress data?

Performance Optimisation and AdministrationMedium
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VertiPaq is the in-memory columnar engine for Import models. It stores each column separately and compresses it using dictionary encoding, which maps unique values to integers, value encoding for numbers, and run-length encoding for repeated sequences. Compression depends mostly on column cardinality, so columns with few unique values compress very well, while unique IDs and precise timestamps take most of the memory.
77

What tools do you use to analyse Power BI performance?

Performance Optimisation and AdministrationMedium
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Performance Analyzer in Desktop records how long each visual takes for DAX query, visual display and other work, and lets you copy the query. DAX Studio runs those queries with server timings and query plans and includes VertiPaq Analyzer for model size by table and column. Best Practice Analyzer in Tabular Editor flags modelling issues. In the Service, capacity metrics apps show load on Premium or Fabric capacity.
78

What does the Best Practice Analyzer do?

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Best Practice Analyzer, in Tabular Editor and also available in Fabric notebooks through semantic link labs, scans a semantic model against a set of rules, such as avoiding bi-directional relationships, hiding foreign keys, not summarising numeric IDs, using DIVIDE, and setting format strings. It lists violations with their severity so teams can fix them before release. Rules can be customised to match team standards.
79

A report page takes 25 seconds to load. Walk me through how you would fix it.

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I would run Performance Analyzer to find the slowest visuals, copy their DAX queries into DAX Studio and check server timings. Common fixes are rewriting measures that iterate large fact tables, removing bi-directional relationships, reducing visuals on the page, and shrinking the model by removing high-cardinality columns. If the source is DirectQuery, I would add aggregations or move to Import. Then re-measure after each change.
80

How do you analyse model size with DAX Studio?

Performance Optimisation and AdministrationMedium
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Connect DAX Studio to the open Power BI Desktop file, go to Advanced, View Metrics to run VertiPaq Analyzer. It shows size per table and column, cardinality, encoding and relationship sizes. Sort columns by total size to find the biggest consumers, often IDs, timestamps or long text. You can export a vpax file to compare before and after optimisation or share with colleagues.
81

Rewrite a slow measure to use variables and avoid repeated calculation.

Performance Optimisation and AdministrationMedium
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Before: Growth = IF([Sales PY] = 0, BLANK(), ([Total Sales] - [Sales PY]) / [Sales PY]) After: Growth = VAR cur = [Total Sales] VAR py = [Sales PY] RETURN DIVIDE(cur - py, py) The previous year measure is now evaluated once instead of three times, and DIVIDE handles zero safely.
82

How do you run a DAX query in DAX Studio to test a measure?

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EVALUATE SUMMARIZECOLUMNS( 'Date'[Fiscal Year], 'Product'[Category], "Sales", [Total Sales], "Margin", [Margin %] ) ORDER BY 'Date'[Fiscal Year] Turn on Server Timings and Clear cache before running to see storage engine and formula engine time. The same EVALUATE syntax works in the DAX query view in Desktop.
83

Split a datetime column to reduce cardinality in Power Query.

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= Table.AddColumn(Source, "OrderDateOnly", each DateTime.Date([OrderDateTime]), type date) = Table.AddColumn(Prev, "OrderHour", each Time.Hour([OrderDateTime]), Int64.Type) Then remove the original OrderDateTime column. A datetime with seconds can have millions of unique values, while date and hour columns have only thousands and 24 values, compressing much better.
84

How do you explain a technical limitation to a business user who wants something impossible?

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I acknowledge the goal, explain the limitation in simple terms and offer an alternative that meets most of the need. For example, when a user wanted live updates every second on a DirectQuery report over a slow system, I explained the load it would create and offered a 15-minute refresh plus an alert for threshold breaches. They accepted because the key decision was covered.
85

What is Copilot in Power BI and what should you watch out for?

Power BI FundamentalsMedium
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Copilot in Power BI uses generative AI to help create report pages, summarise visuals in narrative form, suggest DAX and answer questions about data in natural language. It needs supported capacity and tenant settings enabled by admins. Results depend heavily on a clean model with clear names, descriptions and synonyms, and outputs must be checked for correctness before sharing, especially generated DAX.
86

Tell me about a time you had to deliver a report with unclear requirements.

Power BI FundamentalsMedium
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Situation: an operations head asked for a 'delivery performance dashboard' with no detail. Task: deliver something useful in a week. Action: I held a 30-minute session to list five questions they wanted answered, sketched a page layout and built a quick prototype in two days with sample data. After feedback I finalised it. Result: the dashboard went live on time and became part of the weekly operations review.
87

How do you handle errors in Power Query without failing the whole refresh?

Power Query and Data TransformationMedium
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Use Keep Errors on a copy of the query to inspect the bad rows, then fix the cause, such as wrong data types or invalid dates. Replace Errors can substitute a value, and in M try ... otherwise catches errors per value: = Table.AddColumn(Source, "AmountNum", each try Number.From([Amount]) otherwise null, type nullable number) Log error rows to a separate query so they can be reviewed rather than silently dropped.
88

What is the difference between Group By in Power Query and summarising in DAX?

Power Query and Data TransformationMedium
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Group By in Power Query aggregates rows at refresh time and stores only the summarised table, reducing model size, which is useful when detail is never needed. Summarising in DAX through measures keeps detail in the model and aggregates dynamically for any filter at query time. Use Power Query grouping for fixed summaries such as monthly snapshots, and DAX measures when users need flexible slicing.
89

How do you ensure your report numbers are trusted by finance users?

Visualisation and Report DesignMedium
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I reconcile key measures with the finance system for several periods before launch and document definitions, such as whether revenue is net of returns and taxes, in measure descriptions and a glossary page. I add a refresh timestamp to each page and set up data quality checks. When differences appear, I explain them quickly. Certified semantic models signal that numbers went through review.
90

What is a decomposition tree and when is it useful?

Visualisation and Report DesignMedium
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The decomposition tree is an AI visual that lets users break down a measure across several dimensions in any order, for example splitting a sales drop by region, then category, then channel. It can also suggest the next split automatically using high value or low value analysis. It is useful for root-cause exploration by business users, though it is less suited to fixed reporting.
91

Your workspace has grown to 150 items and nobody knows which reports are used. How do you clean it up?

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I would export usage from the activity log or the workspace usage metrics, list items not viewed in 90 days and confirm with owners before archiving. Duplicate models are consolidated into shared semantic models, naming standards are applied, and workspaces are split by domain with clear owners. A quarterly review keeps it tidy. This also reduces refresh load on capacity.
92

How do you set up an app with different audiences?

Power BI Service, Sharing and SecurityMedium
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In the workspace choose Create app or Update app, add the reports and dashboards, then in the Audience tab create audiences such as Sales Managers and Finance, choose which content each audience sees and grant access to the right Entra ID security groups. Publish the app and share the link. Remember RLS still controls rows inside reports; audiences only control which items are visible.
93

Users need to filter a report by 5,000 product names using a slicer, and it is slow. What do you do?

Performance Optimisation and AdministrationMedium
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A slicer with thousands of values sends heavy queries and is hard to use. I would add a hierarchy so users pick category and subcategory first, enable the slicer search box, and consider a text filter visual for direct search. Apply buttons in query reduction settings stop queries on every click. If the slicer depends on a measure-filtered list, I would simplify that logic.
94

Describe how you would review another developer's Power BI model before release.

Performance Optimisation and AdministrationMedium
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I check the model diagram for a clean star schema and single-direction relationships, run Best Practice Analyzer, and review VertiPaq Analyzer for oversized columns. I read key measures for correctness and naming, check that keys are hidden and formats set, test RLS roles, and run Performance Analyzer on main pages. I share findings as a short prioritised list, explaining why each change matters.
95

Tell me about a time you had to learn a new BI tool or feature quickly for a project.

Power BI FundamentalsMedium
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Situation: a client moved its data to a Fabric lakehouse and wanted reports on Direct Lake within three weeks. Task: learn it and deliver. Action: I studied the documentation, built a small proof of concept in two days, checked fallback behaviour and refresh rules, and then migrated the main sales model. Result: reports went live on time with data visible minutes after loading instead of after nightly refreshes.

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