Prevent Duplicate Data Entry using Cell Validations

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We all know that data validation is a very useful feature in Excel. You can use data validation to create a drop-down list in a cell and limit the values user can enter. But, do you know that you can use data validation in a multitude of ways to prevent users from entering wrong data?

Here is a practical application: Prevent users from entering duplicate values in a range of cells.

For eg. you are making an invoice. Wouldn’t it be cool if Excel prompted you when you enter a duplicate line item so that increase the item quantity instead of repeating it.

Here is a 3 step tutorial to do just that.

Step 1: Identify the range of cells where you want only unique values to be entered

This is simple. All you have to do is find the range where you want to control the user input. Lets say the range is B4:B11

Step 2: Set up Data Validation to prevent duplicate entries

Select the range (B4:B11) and go to data validation (Excel 2007: Data Ribbon > Data Validation, or press ALT+AVV)

Using Data Validation to prevent DuplicatesNow, specify the validation type as “Custom”, this will allow us to use formulas to check for valid data. In our case, we need check if a particular entry is duplicated in the range B4:B11. This can be easily done using COUNTIF formula [learn COUNTIF Formula in plain English].

Go to the formula field and type the countif formula like this: =COUNTIF($B$4:$B$11,B4)<=1

Also, you can set up the “Error Alert” so that you can show a custom message when a duplicate value is typed, like “You have already added that product” message.

Data Validation - Error message

Once you set up error message, it will show up like this:

Data validation to prevent duplicates - error message example
Step 3: Sit back and Relax

The third step is all too familiar. Now that you have prevented duplicate entries in your spreadsheets you can sit back and relax. May be read a few more spreadcheats.

More kickass stuff on data validation (and working with duplicates) using excel

There are a ton of useful articles on the site related to data validation and working with duplicates using excel. Here is a sample. Get started and learn something useful today.

This post is part of our spreadcheats series (yes, the series is still going after one year 😛 )

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17 Responses to “Custom Number Formats – Colors”

  1. Duncan says:

    You are right, Chandoo. I was playing with the colour numbers last week and some of them don't appear different from each other. Others are totally different from yours.

  2. Hui... says:

    @Duncan
    Each version of Excel, post 2003, renders colors slightly differently
    Different language versions may also have different default color palettes

  3. polo says:

    Hello in french
    excel 2010
    colo1 = couleur1 = black
    [couleur1]; [couleur2]; etc..

  4. Andras Ujszaszy says:

    @Hui, thank you very much again for this great post.
    However - under Excel 2007, Hungarian version your solution does not work with color names. I've tried both English and Hungarian names, but drops an error message "not valid formats"

    Do you have any idea how to solve this issue?
    thanks in advance

    • Hui... says:

      @Andras

      Without a Hungarian version of Excel 2003 I don't think I can assist

    • Sarah says:

      Have you tried using the colour numbers? I couldn't get the names to work (despite using an english version of excel). but it did work with the numbers though. I left out the "u" and was easily able to produce burgundy using [color9]

    • Florinel says:

      Here a possible solution: find an English version of Excel, write there the formats using English names, then open the file in the Hungarian version and see the translation.

  5. Nigel says:

    In Excel 2007 I can't get the colour names to work e.g Sea Green but the numbers do e.g color3 - colour3 does not work so I must bow to the country that has stolen my language (ha ha!)

  6. Hey chandoo, nice Tip!
    Wouldn't be easier just apply some conditional formatting for negative numbers and another for positive numbers? Or there's some cases that you can't do that?

  7. Unfortunately the TEXT function doesn't color the cell as number formatting does.

  8. Khalid NGO says:

    Hi Hui,
    Great post Sir, love the new way of formatting with color numbers.
    I am using 2007, and it leads me to the last color number 56.

    Thanks Hui.

  9. […] explains how to set up custom number formats with a wide array of […]

  10. Colin says:

    Thanks Hui - works a treat!

  11. John Smith says:

    Thank you, very helpful.
    Trying to figure out if it is possible to apply color only to a part of the cell?

    E.g. I have a value formatted as Accounting with a currency symbol.
    Those I find somewhat distracting though necessary. If I could make them less obtrusive by coloring them gray while the number would stay black, that would be great. Tried tinkering with the format string, but didn't get the desired result. Single color for complete cell value works, but coloring just part of it could not be achieved. Maybe somebody managed that?

  12. Shaun says:

    Exactly what I was looking for - thank you!

  13. colour in the Australian doesn't work - we have to go American and no problem.
    I always thought is was 56 colours notice you have 57. Cool.

    thanks
    Analir Pisani
    Customised Microsoft Office Training Specialist
    Sydney - Australia
    http://www.azsolutions.com.au

  14. Me Myself says:

    Thank You!

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