# SYSFOREIGNKEYS system table

The SYSFOREIGNKEYS table describes the information specific to foreign key constraints in the current database.

Derby generates a backing index for each foreign key constraint. The name of this index is the same as SYSFOREIGNKEYS.CONGLOMERATEID.

The following table shows the contents of the SYSFOREIGNKEYS system table.

Table 1. SYSFOREIGNKEYS system table
Column Name | Type | Length | Nullable | Contents
--- | --- | --- | --- | ---
CONSTRAINTID | CHAR | 36 | false | Unique identifier for the foreign key constraint (join with SYSCONSTRAINTS.CONSTRAINTID)
CONGLOMERATEID | CHAR | 36 | false | Unique identifier for index backing up the foreign key constraint (join with SYSCONGLOMERATES. CONGLOMERATEID)
KEYCONSTRAINTID | CHAR | 36 | false | Unique identifier for the primary key or unique constraint referenced by this foreign key (SYSKEYS.CONSTRAINTID or SYSCONSTRAINTS.CONSTRAINTID)
DELETERULE | CHAR | 1 | false | 'R' for NO ACTION (default), 'S' for RESTRICT, 'C' for CASCADE, 'U' for SET NULL
UPDATERULE | CHAR | 1 | false | 'R' for NO ACTION (default), 'S' for RESTRICT

Parent topic: Derby system tables