Which operator reduces the number of search results in a database query?

The operator that reduces the number of search results in a database query is AND. This operator is used in database searches to ensure that all specified search criteria must be met in the results. When you use AND between search terms, the database returns only those entries that contain all the terms included in the query, thus narrowing down the results to more specific instances that align with the criteria defined by the search terms. For instance, a search for "social work" AND "mental health" will yield results that include both terms, significantly reducing the overall number of entries compared to using OR, which broadens the results by including records containing either term. This specificity is crucial in research, including social work practice, as it helps focus on the most relevant information.