Preventing Duplicate Entries within a table column

Hello! Peter. Thanks for the details. You’re on the right track with COUNTIF, but you’re running into the usual problem: fixed ranges don’t expand or shrink with the table. Since you’re using a structured table (tblDataEntry), you can make the validation dynamic.

Here’s how you can do it:

Option 1: Use Structured Reference in Data Validation

1. Select the whole column of your table where you want to prevent duplicates (e.g. tblDataEntry[No.]).
2. Go to Data → Data Validation.
3. In Allow choose Custom.
4. Enter this formula: =COUNTIF(tblDataEntry[No.],[@No.])=1 Explanation:
   • tblDataEntry[No.] → the whole column of the table.
   • [@No.] → the current row’s value.
   • COUNTIF(...)=1 ensures the value only appears once in the column.
   This will expand/shrink as your table grows.

Option 2: With INDIRECT (if structured references don’t work in validation)

Sometimes Excel rejects structured references in Data Validation. In that case, wrap it like this:

=COUNTIF(INDIRECT("tblDataEntry[No.]"),A7)=1

(where A7 is the first data row cell in your table’s No. column). Then apply it to the whole column of the table.

Option 3: Using UNIQUE (Excel 365+ only)

If you’re on Office 365, you can simplify with:

=COUNTIF(tblDataEntry[No.],[@No.])=1

Or validate against a dynamic spill range of unique values, but Option 1 is usually the cleanest.

See if this helps. If you need further assistance, just let me know.

Best regards,

Kimberly