Here is a very simple way, ShamsulZ!

Imagine you are typing in column A.
Add a new column B, and use the formula =COUNTIF(A:A,A2) in cell B2. Extend
it downwards. This will tell you how many times each item occurs.

You can then sort or filter on column B for anything that is not 1.

--
Allllen


"ShamsulZ" wrote:

how to know that I'm not key-in the data twice or more in one worksheet? In
my daily job, there is thousands of data and the data cannot duplicate.
Thanks a lot friend.