In order to make your data more reliable, you can prohibit the generation of duplicates.
I want each contact in my CRM to be unique. Therefore, filling in an existing contact will result in an error message and my contact will not be created.
Go to the table options :
Select Organize fields or in the advanced option of the configurator of the column "part of the unique key" :
Check the box "Unique key" of the desired column :
You can of course assign the option to multiple columns in the same table.
This will create a concatenation of these fields in order to create a unique key and thus prevent the creation of duplicates on this key composed of several fields.