The problem of counting the number of matches between two columns in Excel arises when we have two lists of data and want to find out how many items appear in both lists. For example, suppose we have a list of employee names in column A and a list of names of employees who have completed a training course in column B. We want to know how many employees have completed the training course and are also on the list of all employees.

## Using the COUNTIF Function

The easiest way to count the number of matches between two columns in Excel is by using the COUNTIF function. The COUNTIF function counts the number of cells within a range that meet a specified condition. In this case, the condition is that the value in a cell in column B appears in column A.

To use the COUNTIF function, use the formula below:

`=COUNTIF(A:A,B1)`

The formula will count the number of times the value in cell B1 appears in column A. To count the number of matches for all values in column B, copy the formula down to the other cells in the column.

## Handling Multiple Matches

If a value appears multiple times in both columns, the COUNTIF function will count each match separately. For example, if the name “John” appears twice in column A and once in column B, the formula =COUNTIF(A:A,B1) will return a count of two.

To count only unique matches, we can use the combination of the IF and COUNTIF functions. The following formula counts only the unique matches:

`=SUM(IF(COUNTIF(A:A,B:B)>0,1))`

This formula works by first using the COUNTIF function to count the number of times each value in column B appears in column A. If a value appears more than once, its count will be greater than zero. The IF function then checks if the count is greater than zero and returns a value of 1 if it is. Finally, the SUM function adds up all the ones, giving us the total count of unique matches.

## Dealing with Case Sensitivity

By default, the COUNTIF function is case-insensitive. This means that it treats uppercase and lowercase letters as equivalent. If we want to make the function case-sensitive, we can use the SUMPRODUCT function instead of the COUNTIF function. The following formula counts only the unique matches and is case-sensitive:

`=SUMPRODUCT((A:A=B:B)*(A:A<>""))`

This formula works by first checking if the value in column B is equal to the value in column A, and then checking if the value in column A is not empty. The * operator performs a logical AND operation between the two checks, which returns a value of 1 if both checks are true. The SUMPRODUCT function then adds up all the ones, giving us the total count of unique matches.

Thank you.