In a left outer join, what happens to unmatched records from the target layer?

In a left outer join, unmatched records from the target layer are included in the result set as null values. This means that all records from the primary layer (the left table) will be retained in the output, while any corresponding records from the target layer that do not have a match will have their fields populated with null values. This feature is essential because it allows users to preserve all entries from the primary layer and easily identify where data is missing from the target layer, enabling further analysis or decision-making based on the full context of the primary dataset.

For instance, if you are merging two datasets where you're interested in retaining all the information from the primary dataset, even if some records do not find a matching record in the secondary dataset, this operation allows you to see gaps or missing associations effectively. Other options such as discarding the unmatched records or triggering an error fundamentally alter the nature of the join, thereby not serving the purpose of a left outer join, which is to maintain a complete view of the primary data set while providing additional context from the target dataset.