14. "Drag and Drop" the dsEmployeeList either from the Data Explorer or from
the Outline.
Report Parameters
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15. Preview the Report.
Now, when you bring up the Show Report Parameters Dialog, you can see that you
have a drop-down list with all the possible jobs for the employees. When you select
one and hit OK, it will filter down to employees with that job.
The example just explained used a database Data Set instead of one of the static
ones. In case of a database, you usually want to use a Data Set Parameter instead of
a Filter. Using a "where" clause and a Data Set Parameter will always outperform a
Filter, as the data is being filtered on the end of the DBMS. The DBMS is much more
efficient at filtering data than BIRT would be. If you pulled a large Data Set, BIRT
would have to retrieve that entire Data Set and apply the filter to it, wasting network
bandwidth and processing time. Filters are useful in cases where you don't have a
database to work with, such as a text file Data Source, or XML Data Source. In those
cases, there is no DBMS to process a "where" clause and you have no choice but to
use a Filter. However, in either case, we have seen how the user can influence the
data that gets returned, as the last example will apply to the scripted Data Source,
the flat file Data Source, and the XML Data Source.
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