This optional clause defines the relationship between a UDF or external stored procedure and data that is external to Vantage.
The option you specify determines:
- Whether or not the external routine can read or modify external data
- Whether or not the database will redrive the request involving the function or procedure after a database restart
If Redrive protection is enabled, the system preserves responses for completed SQL requests and resubmits uncompleted requests when there is a database restart. However, if the External Data Access clause of an external routine is defined with the MODIFIES EXTERNAL DATA option, then the database will not redrive the request involving that function or procedure. For details about Redrive functionality, see:
- Teradata Vantage™ - Database Administration, B035-1093
- The RedriveProtection and RedriveDefaultParticipation DBS Control fields in Teradata Vantage™ - Database Utilities, B035-1102.
If you do not specify an External Data Access clause, the default is NO EXTERNAL DATA.
The following table explains the options for the External Data Access clause and how the database uses them for external routines.
|MODIFIES EXTERNAL DATA||The routine modifies data that is external to the database. In this case, the word modify includes delete, insert, and update operations.
Following a database failure, the database does not redrive requests involving a function or external stored procedure defined with this option.
|NO EXTERNAL DATA||The routine does not access data that is external to the database. This is the default.|
|READS EXTERNAL DATA||The routine reads, but does not modify data that is external to the database.|