How to set up access queries to prevent duplications?

In Access, you can use the DISTINCT keyword to set unique results.

In the query design view, open your query and select the fields you want to query. Then, go to the “Properties” tab on the query design toolbar and choose “Yes” in the “Unique Values” column.

Another way is to use the GROUP BY clause. In the query design view, select the fields you want to query, drag them to the bottom of the query design window. Then, in the “Total” line, select “Group By” and choose the fields to group by. This will ensure that there are no duplicate values in the results.

Please note, using the DISTINCT keyword or GROUP BY clause may impact the performance of the query, especially when dealing with a large amount of data. In such cases, you may need to consider using indexes or optimizing the query to improve performance.