A Reference Index is an internal structure that the system creates whenever a referential integrity constraint is defined between tables using a PRIMARY KEY or UNIQUE constraint on the parent table in the relationship and a REFERENCES constraint on a foreign key in the child table. Teradata Database does not create or maintain REFERENCE indexes for batch referential integrity relationships.
The index row contains a count of the number of references in the child, or foreign key, table to the PRIMARY KEY or UNIQUE constraint in the parent table.
A maximum of 64 referential constraints can be defined for a table. Similarly, a maximum of 64 tables can reference a single table in a referential constraint. Therefore, there is a maximum of 128 Reference Index descriptors that can be stored in the table header per table.
However, the Reference Index subtable for a table stores only the Reference Indexes that define its relationship with its child tables, so only 64 Reference Indexes are stored in the subtable per base table.
Apart from capacity planning issues, Reference Indexes have no user visibility.
For information about reference index sizing issues, see “Reference Index Sizing Equation” on page 867.