Which DAX function can be used to count the number of distinct values in a column?

The function that is specifically designed to count the number of distinct values in a column is DISTINCTCOUNT. This function evaluates the specified column and returns the total number of unique values it contains, ignoring any duplicates. This capability is particularly useful when analyzing data to derive meaningful insights where understanding the distinct contributions of different categories or values is essential.

Other functions such as SUMMARIZE and COUNT have different purposes. SUMMARIZE is used to create a summary table for the specified groups, which is useful for aggregating data but does not specifically count distinct values. COUNT, on the other hand, simply counts rows in a column that contains non-blank values, without consideration of whether those values are distinct or not. Therefore, DISTINCTCOUNT is the function tailored to the need for counting unique entries, making it the correct choice for this scenario.