Sometimes it is necessary to lookup a value from one table to bring into another. For example, knowing how much a Market Campaign costs versus the Opportunity amount is a figure of value.
These two amounts typically reside in different systems. So we need to lookup the value from the Marketing system and bring it into the main Sales table.
Taking the Sales Opportunities table, we can create a custom field that will allow us to lookup a value from the Marketing Campaigns table based on the Marketing Campaign ID.
We make the Marketing Campaigns table Invisible as we only need the one field in our Sales Opportunities table. As there is only One Marketing Campaign ID per Opportunity ID, this is known as a 1 to 1 relationship.
*You can learn more about this feature in this Link