Understanding the Differences Between Ranges and Filters

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Both ranges and filters restrict visible records to a subset of all available records, but the way they do so differs. A range is a set of contiguously indexed records that fall between specified boundary values. For example, in an employee database indexed on last name, you might apply a range to display all employees whose last names are greater than "Jones" and less than "Smith". Because ranges depend on indexes, you must set the current index to one that can be used to define the range. As with specifying an index to sort records, you can assign the index on which to define a range using either the IndexName or the IndexFieldNames property.

A filter, on the other hand, is any set of records that share specified data points, regardless of indexing. For example, you might filter an employee database to display all employees who live in California and who have worked for the company for five or more years. While filters can make use of indexes if they apply, filters are not dependent on them. Filters are applied record-by-record as an application scrolls through a dataset.

In general, filters are more flexible than ranges. Ranges, however, can be more efficient when datasets are large and the records of interest to an application are already blocked in contiguously indexed groups. For very large datasets, it may be still more efficient to use the WHERE clause of a query-type dataset to select data. For details on specifying a query, see Using Query-type Datasets.

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