What function can be used to calculate the sum of a column in DAX?

The function used to calculate the sum of a column in DAX is SUM. This function is straightforward and efficient, specifically designed to aggregate numerical data by adding up all the values within a specified column. When you apply the SUM function, it evaluates the entire column and returns a single value that represents the total of all entries.

The other functions mentioned serve different purposes. SUMX, for instance, is an iterator function that evaluates an expression for each row in a table and then returns the sum of those values, which is useful when you need to calculate a sum based on complex calculations for each row rather than just summing up a column directly. CONCATENATE is used to join two text strings into one and is not applicable for numerical aggregation. CALCULATE modifies the filter context for calculations and can be used with SUM, but by itself does not directly compute sums without an accompanying aggregation function.

Thus, using the SUM function is the most appropriate and direct means of summing a column in DAX.