|Managing Your Data in GemFire XD / Exporting and Importing Data with GemFire XD|
Table functions are functions that package up external data to look like GemFire XD tables. The external data can be an XML file, a table in a foreign database, a live data feed--in short, any information source that can be presented as a JDBC ResultSet.
A GemFire XD table function lets you efficiently import foreign data into GemFire XD tables. Table functions let you join GemFire XD tables with any of the following data sources:
The data imported by a table function acts like a GemFire XD replicated table that has no indexes. All data is fetched on every GemFire XD member where a query against the table is executed. Outer joins that involve a partitioned table and a table function have limitations similar to joins with replicated tables (duplicate values are returned from the replicated table or table function).
See ../../reference/language_ref/ref-create-function.html#create_function for the complete syntax needed to declare GemFire XD table functions. The following topics provide information on how to write Java methods that wrap foreign data sources inside JDBC ResultSets.