The DISTINCT function in DAX is used to return a unique list of values from a column or table — it removes duplicates and gives you only distinct entries. Essentially, it’s a way to create a deduplicated version of your data for further calculations.
The syntax is simple:DISTINCT(<column or table>)
For example, if I have a Sales table with a CustomerID column where some customers appear multiple times, and I want to count how many unique customers made purchases, I can write:Unique Customers = COUNTROWS(DISTINCT(Sales[CustomerID]))
This expression first returns a table of distinct customer IDs, then counts how many rows that table has — effectively giving the number of unique customers.
In one of my Power BI dashboards, I used DISTINCT to calculate the number of unique products sold. Since the same product appeared multiple times in different transactions, COUNTROWS(DISTINCT(Sales[ProductID])) gave me the exact count without duplication.
A challenge I faced with DISTINCT was when the dataset was very large — using DISTINCT on millions of rows can slow down the model because it internally creates a temporary table. To optimize performance, I sometimes pre-aggregate data in Power Query or use the VALUES function instead, which behaves similarly but can work better with filters.
The main difference between DISTINCT and VALUES is that DISTINCT always removes duplicates, while VALUES also includes a blank row if the column contains blanks — which can be useful for handling incomplete data.
So, in short — DISTINCT is used to get a clean list of unique values from a column or table, commonly used for unique counts, validation, or to create filtered tables for further calculations. It’s simple but very powerful when you need to eliminate duplicate records in DAX expressions.