Display an alert if data already exists

[c3rn_nz]

Hi everyone, I require some help creating an alert please.

The situation is as follows.
- I have a workbook called Invoices
- There are two sheets in the workbook, one called Current and the other called Processed
- Users enter in pertinent details daily and then a certain user processes the data and moves (cut/paste) the entries from the Current sheet to the one called Processed.
- In column B, users enter an invoice number

I would like to create an alert for when a user enters an invoice number in any row of column B and that invoice number already exists in column B across either of the two sheets.

Ideally a pop up would be displayed, just providing a warning. The user can then choose to close the warning/pop up and continue if they wish.

Any assistance in this matter would be appreciated.

 

[c3rn_nz]

Ok so I tried both of the codes supplied but they didn't seem to work. Perhaps I'm not entering them correctly (my first time inserting a macro).

This is how I have it set up in Visual Basics editor. However when I close the editor and purposely try to enter an invoice number that exists, no alerts occur.

What am I doing wrong?

 

[Yongle]

from VBA window
In the picture you posted , each sheet is listed in window pane on left
- double click on sheet Current and place code in that module

OR from EXCEL
- right-click on the sheet tab for sheet Currrent \ View Code \ paste code into the window which appears

The alert occurs when invoices are entered in sheet Current

 

[c3rn_nz]

Perfect that fixed it. Working great.

Thank you all again for your assistance.