Connecting to External Databases

The database reader can be used to read rows from nonspatial databases, such as Microsoft Access, ODBC, and Oracle. Database reader feature type properties allow you to specify a complete and arbitrary SQL SELECT statement to be used to determine the features that will be returned. Click the Feature Type Parameters tab. The SELECT statement can involve joins to other tables in additional to filtering data from a single table. As well, the parameters tab allows for a WHERE clause to filter the features that are extracted. If the attribute data is held in CSV or dBase III files, then the CSV or dBase readers can be used to directly read the data. No filtering via a WHERE clause is available in these cases. Using a database reader in conjunction with another reader of feature data and the FeatureMerger transformer, can in some situations be more efficient than using the Joiner or SQLExecutor. This is because the Joiner and SQLExecutor make queries of the database for each feature that passes through them. However, if the relevant parts of the database can be identified ahead of time and read in a single query by a database reader, and the resulting attribute features routed to a FeatureMerger transformer as SUPPLIER features, they can efficiently be paired up to the feature data acting as a REQUESTOR in the FeatureMerger.