Build a star schema from a single flat file
One wide CSV, thousands of repeated names. By the end you have a fact table, two dimension tables, and a model Power BI actually wants.
Data Modeling
// 24 postsTutorials, tips, and deep dives on Data Modeling — every post from bianca.codes tagged Data Modeling.
Data Modeling posts
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VAR: the DAX keyword that makes your measures readable
A DAX measure that repeats the same subtotal three times isn't thorough, it's a maintenance problem VAR was built to fix.
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Most Power BI dashboards are just decorated spreadsheets
Three slicers and a card don't turn a spreadsheet into a data model, and the columns you didn't build are exactly where it falls apart.
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The dashboard I built that nobody opened
Three months of polish, a great demo, and a usage metrics report that told a very different story once the meeting was over.
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When did the spreadsheet quietly become a database - and why that's a problem
Nobody decided to build a database out of that 80-tab workbook - it ended up doing a database's job without any of a database's guarantees.
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Star Schema Done Right, Part 4: Migrating a Flat Table to a Star Schema in Power BI
Power Query carves one flat sales table into a fact and three dimensions, you build the relationships, and you prove the numbers didn't move - a restructure you can't validate is just hope.
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Star Schema Done Right, Part 3: Slowly Changing Dimensions - The Bit Nobody Explains
A customer moves and changes tier, and some reports should show where they are now while others must show where they were at the sale - the gap is a modelling decision most tutorials skip.
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The Part of Data Modelling Everyone Skips (That Breaks Everything Later)
Your measure is right, your data reconciles, and your year-to-date is still wrong - because the model never had a real date table, only a date column pretending to be one.
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Star Schema Done Right, Part 2: Dimension Tables and Why Cardinality Matters
A dimension table isn't just a lookup. Why fact-to-dimension relationships have to be many-to-one, why bidirectional filtering always causes problems, and how to build dimensions your DAX can trust.
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REDUCE: How to Build Running Calculations Across Any Dimension in Excel
REDUCE is the most powerful of the functional array functions and the most overlooked. The lambda which means you can accumulate strings, and replace calculations that used to need VBA.
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Star Schema Done Right, Part 1: What a Fact Table Actually Is (And Isn't)
Most introductions to star schema start with the diagram. The star, the centre, the spokes. This one starts with the question: what problem does a fact table solve that a flat table doesn't? Part 1 builds the intuition before the vocabulary, so the rest of the series makes immediate sense.
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Excel Is Quietly Becoming a Programming Language and Most Users Haven't Noticed
LAMBDA, MAP, REDUCE, SCAN, BYROW. These are functional programming primitives. Excel is shipping them one by one, and most users are still writing nested IFs. The spreadsheet you learned in 2015 has been quietly replaced by something much more powerful.
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Build a Dynamic Data Validation List That Updates Itself When Your Source Table Grows
You'll build a dropdown list that reads from a structured table and includes every new row automatically. No named range maintenance, no 'why isn't my new entry showing up' moments.
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Your Power BI Report's Performance Problem Is Probably Your Data Model, Not Your DAX
Slow reports get blamed on complex measures. Complex measures get rewritten. And the report is still slow — because the actual problem is a flat table with 47 columns, many-to-many relationships, a…
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The Excel Functions Your Spreadsheet Has Been Missing for Ten Years
XLOOKUP, LET, LAMBDA, BYROW, SCAN, MAP — Microsoft shipped more genuinely useful functions in the last three years than in the previous decade. If you learned Excel before 2022 and haven't revisite…
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Getting Credit for Work That 'Looks Easy'
The more competent you get, the less people see the effort behind what you deliver. A clean dashboard looks effortless. A fast turnaround looks like it was always fast.
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The Difference Between a Dashboard and a Decision Tool (And Why It Matters)
Most dashboards answer the question 'what happened?' Very few answer 'what should we do?' The gap isn't data — it's intent. A dashboard built for the former often actively gets in the way of the la…
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When Your Manager Doesn't Understand What You Built
You delivered a clean model, a solid dashboard, a real solution — and got a blank look in the room. The work was right. But explaining technical work to someone who doesn't share your frame of refe…
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DAX Context Demystified, Part 3: Time Intelligence and Why Your YTD Is Probably Wrong
Time intelligence functions look simple - TOTALYTD, SAMEPERIODLASTYEAR — until they aren't. The reason they break isn't the function. It's that context transition interacts with your date table…
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Avoid Bragging: Talk About Your Work Effectively
Stop cringing. There's a way to talk about your accomplishments in Excel and Power BI that sounds competent, not arrogant. It's all about framing.
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DAX Context Demystified, Part 2: CALCULATE and Context Transition
CALCULATE is the most powerful function in DAX - and the most misunderstood. Once you see how it deliberately replaces the filter context rather than adding to it, every confusing measure result …
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Build a One-Page Executive Dashboard in Power BI That Stakeholders Actually Open
You'll build a clean single-page report: KPI cards, a trend line, and one slicer. The kind that gets opened voluntarily, not just emailed as a screenshot. Starting from a blank canvas, ending with …
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Why 'Just Learn SQL' Is the Wrong Advice for Most Excel Users
The advice is everywhere: if you're serious about data, you need SQL. But for most analysts already working in Excel and Power BI, the gap isn't SQL knowledge - it's data modelling instinct. Here…
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DAX Context Demystified, Part 1: Row Context vs Filter Context
DAX's context confusion cost me hours. Turns out, it's just two simple ideas.