use of Unique in mySQL field cases Error

I want to limit the values in one varchar field  in mySQL  to be unique. I am finding that when my code tries to add another copy of the same varchar I get 


ERROR - 2020-07-21 00:13:54 --> Query error: Duplicate entry 'software engineer' for key 'item' - Invalid query: INSERT INTO `exclude` (`item`, `campaign`, `userid`) VALUES ('software engineer', 'Apple', '[email protected]')

I do want to not allow a duplicate, but I don't want an error to occur when an attempt is made. How can I inhibit the ERROR message? 

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