There are several ways to find duplicate customer IDs in a dataset using Excel formulas. Here are a few examples:

**#1: Using the COUNTIF function:**

You can use the COUNTIF function to count the number of times a customer ID appears in the dataset. If the count is greater than 1, it means that the ID is a duplicate.

**Here’s the formula: =COUNTIF(A2:A10, A2)**

This formula will count the number of times the customer ID in cell A2 appears in the range A2:A10. You can drag this formula down to the rest of the cells in column A to check for duplicates in the entire dataset.

**#2: Using the IF and COUNTIF functions:**

You can use the IF and COUNTIF functions together to create a formula that returns “Duplicate” for duplicate customer IDs and “Unique” for unique IDs.

**Here’s the formula: =IF(COUNTIF(A2:A10, A2)>1, “Duplicate”, “Unique”)**

This formula will check the count of the customer ID in cell A2 in the range A2:A10. If the count is greater than 1, it will return “Duplicate”. Otherwise, it will return “Unique”. You can drag this formula down to the rest of the cells in column A to check for duplicates in the entire dataset.

**#3: Using the COUNTIF and SUMPRODUCT functions:**

You can use the COUNTIF and SUMPRODUCT functions together to create a formula that returns the number of duplicate customer IDs in the dataset.

**Here’s the formula: =SUMPRODUCT((COUNTIF(A2:A10, A2:A10)=1)*1)**

This formula will count the number of times each customer ID appears in the range A2:A10, and then sum up the IDs that appear only once (i.e., the unique IDs). The result will be the number of duplicate IDs in the dataset.

**#4: Using the COUNTIF, IF, and ROW functions:**

You can use the COUNTIF, IF, and ROW functions together to create a formula that returns the row numbers of the duplicate customer IDs in the dataset.

**Here’s the formula: =IF(COUNTIF(A$2:A$10, A2)>1, ROW(), “”)**

This formula will check the count of the customer ID in cell A2 in the range A2:A10. If the count is greater than 1, it will return the row number of the cell. Otherwise, it will return an empty string. You can drag this formula down to the rest of the cells in column A to check for duplicates in the entire dataset.

**#5: Using the COUNTIF and INDEX functions:**

You can use the COUNTIF and INDEX functions together to create a formula that returns the customer IDs that are duplicates in the dataset.

**Here’s the formula: =IF(COUNTIF($A$2:$A$10, A2)>1, INDEX($A$2:$A$10, ROW()), “”)**

This formula will check the count of the customer ID in cell A2 in the range A2:A10. If the count is greater than 1, it will return the customer ID. Otherwise, it will return an empty string. You can drag this formula down to the rest of the cells in column A to check for duplicates in the entire dataset.

**#6: Using the COUNTIF and IFERROR functions:**

You can use the COUNTIF and IFERROR functions together to create a formula that returns the customer IDs that are duplicates in the dataset, and replaces any errors with an empty string.

**Here’s the formula: =IFERROR(IF(COUNTIF($A$2:$A$10, A2)>1, A2, “”), “”)**

This formula will check the count of the customer ID in cell A2 in the range A2:A10. If the count is greater than 1, it will return the customer ID. If there is an error (e.g., if the cell is blank), it will return an empty string. You can drag this formula down to the rest of the cells in column A to check for duplicates in the entire dataset.