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One of the major concerns of any of the list is tracking information, whether it's about people or transactions, orders as we see here, is the uniqueness of certain columns. We don't want any duplicates whatsoever in column A. Each row here is about a different transaction so we want to prevent duplicate entries. In column A we are going to using the Data Validation capability in Excel. It's on the Data tab. Now let's just talk a little bit about what we want to do here. We want to say, in effect, every time an entry goes in here, we want to make sure that it doesn't exist else where in the column.
So about that, we are going to have five or six, or ten or hundreds of these. At any given time when we make an entree, we want to check that entry with all the others. A different way to say this would be let's use the CountIf function to see how many times the current entry appears in the column and if it appears more than once, prevent it. Column A, Data > Data Validation. The Settings. We want to allow, and there appears to be no real obvious choice here. It's Custom meaning a custom formula.
And here is that custom formula, =countif. Now perhaps you are familiar with this function. It's a great tool for counting the occurrence of entries in a column or a row. And where are we looking here? We're looking in column A so I am going to click that. Comma. A1 is currently the active cell so we use that here as a surrogate or substitute for all the others. And what we are suggesting here is we are going to count the current entry and compare with every thing else in column A to see how many times it occurs, and we want this result to always be 1.
So every time we make a new entry we want to be in effect checking to make sure that it appears every once and only once. So this is the requirement here. So lets try this. Suppose our transactions are truly numbers. There is a 23456, the 34567. How about another 23456? Not valid. We could customize this message if we want to, but I think most people will get the point it's a duplicate here. Cancel.
It also works with letters or letters combinations. Suppose there is a letter scheme, ABCDE, SDERT, ABCDE, there we go, once again it's prevented. So you have control over it. And again that formula, we don't see it here in any of the cells. I'll click back in column A, go back to Data Validation, and there is that formula. If you're familiar with Count If, it's more obvious as to how it works. If you're not, well use it any way because it does work.
Great way to keep out duplicates in column A in this example.
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