About Federated Queries

Data virtualization makes it possible to execute federated queries, which are queries against multiple data sources. Each of these data sources may be of a different type, or of the same type with different settings. In addition, TDV can execute any of almost 300 functions natively when required, making TDV itself a source of federated query results.

The following table lists where in the documentation you can find further information about such issues.

Federated Query Topic	Where Discussed
Data source function support (push vs. no-push)	Function Support for Data Sources section of the TDV Reference Guide.
Suppressing push of SQL operators	The DISABLE_PUSH sections of TDV Query Engine Optimizations.
Pushing custom functions	Pushing a Custom Function to the Native Data Source.
TDV function support	TDV Support for SQL Functions section of the TDV Reference Guide.
Case-sensitivity and trailing spaces in comparisons	See the TDV Administration Guide. “Case Sensitivity and Trailing Spaces” section, CASE_SENSITIVE and IGNORE_TRAILING_SPACES option sections, and Case sensitivity and Ignore Trailing Spaces configuration parameters in the TDV Reference Guide.
Miscellaneous function support issues, such as data precision, truncation vs. rounding, collation, time zones, and interval calculations	Function Support Issues when Combining Data Sources section of the TDV Reference Guide.