About filtering options
You can filter data at the data set level and at the table level. Filtering at the data set level narrows the scope of data available to a report design and can improve design-time performance if the data set returns a particularly large amount of data. Filtering at the table level narrows the scope of data displayed in a table and is the typical filtering option.
If you filter data at both the data set and table levels, BIRT Studio executes the filter at the data set level first, then at the table level. Design the filters accordingly. For example, if a data set returns all customer sales for ten years, you can create a filter at the data set level to limit the sales data to the current year. Then, when you design your report, you can create a filter at the table level to display sales data for a particular quarter in the current year. You cannot display sales data for the previous year, because the filter at the data set level excludes this data.

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