Since its early versions, 4th Dimension lets you create sets that represent query results on one or several tables. The notion of sets is interesting on several levels: sets allow you to store query results, and, thanks to operations on sets (union, intersection and difference), you can perform queries in sequential steps and combine the results. This allows you to perform more complex queries, and makes them easier to write and maintain. Since version 6, 4th Dimension also lets you use named selections. The principle is
similar to that of sets but with several noticeable differences. This technical note provides methods that let you handle selections as you would sets. These methods illustrate how easy it is create your own commands to adapt to your specific needs.
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