There is a three column database with month in column A, numbers in column B and names in column C. I want to count unique numbers in column B for a specific month and name provided by the end user.
Depending upon the version of MS Excel which you are using, there could be two ways to solve this problem
Solution for MS Excel 2010 and higher versions
If you are using the PowerPivot add-in, then a simple DAX formula can solve this problem.
Solution for all versions of MS Excel
While this solution works for all versions of MS Excel, it uses an array formula (Ctrl+Shift+Enter). Array formulas, if used extensively in the workbook, adversely effect the system’s performance.
You may refer to both solutions in this workbook.
To count unique values with conditions on large databases, you may refer to the following link