If you have exported your search results from a database into Zotero (reference management software) or an Excel spreadsheet, you will probably want to check whether you have any duplicate records, particularly if you are completing a systematic literature review.
In Zotero:
Click "duplicate items" under "My Library" on the left hand side of your Zotero screen
Zotero will identify and group the duplicate records together
If you are happy they are genuine duplicates, click "merge" on the right hand side of the screen
In Excel:
Open the spreadsheet containing your search results
Select the relevant data in your spreadsheet
Click the "data" tab at the top of the screen
Under "data tools", click "remove duplicates"
Select which column(s) you want Excel to check - usually the article title
Click "OK"
Excel will remove exact duplicates. You will see a dialog box informed you how many duplicates have been removed, and how many unique records remain.