Challenge
You've established a relationship between the Date column in your Fact Table and the Calendar Table, but for some reason, the data is not filtering correctly by date.
You’re scratching your head, unable to figure out why the relationship isn’t working.
Solution
The issue is actually very simple—so simple that it might make you feel a bit foolish once you spot it!
Steps to Fix
Go to Power Query
Open your Fact Table in Power Query.
Check the data type of your Date column.
Ensure the Date Column is in 'Date' Format
If the column is in Date/Time format, change it to Date.
Apply & Close Power Query
Load the data again into Power BI.
Your relationship should now work perfectly.
What Not to Do
🚫 Do NOT just format the column in Power BI (via the Modeling tab).
Formatting it as a Date doesn’t actually change the underlying data type—it remains Date/Time, which causes relationship mismatches.
Instead, change its nature in Power Query, where the transformation is permanent.
Alternative Fix (If Not Using Power Query)
Create a New Column in Power BI
But avoid using the FORMAT function
Explanation in More detail
🚫 Do NOT just format the column in Power BI
Let me explain this step by step, so it’s crystal clear.
Why You Might Think Formatting Works (But It Doesn't)
When you see a column showing Date/Time, you might think:
"Oh! I’ll just go to the Modeling tab and change it to 'Date' format. That should work, right?"
Wrong.
What actually happens is:
Power BI only changes how the date LOOKS on your screen.
It does NOT change the actual data type stored inside the table.
Think of it like wearing a costume. If you dress as Spider-Man, people might think you’re Spider-Man, but underneath, you’re still you. Power BI does something similar—it disguises the Date/Time as just Date, but deep down, it’s still storing the Time portion.
Why This Creates a Problem
Power BI relies on exact matches when making relationships between tables.
Let’s say your Fact Table has dates like this:
2024-01-01 12:34:56
2024-01-02 08:45:12
2024-01-03 18:20:30 And your Calendar Table has dates like this:
2024-01-01
2024-01-02
2024-01-03 Even though they look the same to you after formatting, Power BI sees them differently:
💡 Power BI’s Thinking Process:
"Oh! The Fact Table date is 2024-01-01 12:34:56, but the Calendar Table date is only 2024-01-01."
"These are NOT the same! I can’t match them."
"The relationship is broken! I don’t know how to filter correctly."
That’s why filtering by date doesn’t work even though they look fine to you.
The Right Way to Fix It
✅ Go to Power Query and change the column type to ‘Date’ instead of ‘Date/Time’.
This removes the hidden Time part permanently.
Power BI will now store only the pure date, making the relationship work correctly.
Why Power Query is Different from the Modeling Tab
Power Query actually modifies the underlying data before it even reaches Power BI.
The Modeling tab only changes how the data is displayed—it does NOT modify how Power BI stores it.
The Bottom Line
🚫 Don’t just format the column in the Modeling tab—it’s like using makeup to hide a problem instead of fixing it.
✅ Change the data type in Power Query—this ensures Power BI correctly understands and matches the dates.
Now, your relationships will work perfectly, and you won’t be stuck wondering why your filters are broken! 🚀
Summary
🔹 Root Cause: Your Date column is in Date/Time format instead of Date.
🔹 Best Fix: Change the data type in Power Query (recommended).
🔹 Avoid: Formatting the column in Power BI, or using FORMAT() in DAX.
Fix it right, and everything works smoothly again! 🚀
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