The SYS_REFERENTIAL_CONSTRAINTS table is intended for additional information about foreign keys. dotConnect for Google BigQuery doesn't return foreign keys, so this table is always empty. It has the following columns:

Column Name	Data Type	Description
CONSTRAINT_CATALOG	VARCHAR(128)	The Google Cloud project that contains the constraint.
CONSTRAINT_SCHEMA	VARCHAR(128)	The dataset that contains the constraint.
CONSTRAINT_NAME	VARCHAR(128)	The name of the foreign key constraint.
UNIQUE_CONSTRAINT_CATALOG	VARCHAR(128)	The Google Cloud project that contains the referenced constraint.
UNIQUE_CONSTRAINT_SCHEMA	VARCHAR(128)	The dataset that contains the referenced constraint.
UNIQUE_CONSTRAINT_NAME	VARCHAR(128)	The name of the referenced constraint.
MATCH_OPTION	VARCHAR(7)	The match option of the foreign key.
UPDATE_RULE	VARCHAR(9)	The update rule of the foreign key.
DELETE_RULE	VARCHAR(9)	The delete rule of the foreign key.
OBJECT_CATALOG	VARCHAR(128)	The Google Cloud project that contains the table this foreign key belongs to.
OBJECT_SCHEMA	VARCHAR(128)	The dataset that contains the table this foreign key belongs to.
OBJECT	VARCHAR(128)	The name of the table this foreign key belongs to.
FIELD	VARCHAR(128)	The foreign key column.
RELATED_OBJECT_CATALOG	VARCHAR(128)	The Google Cloud project that contains the referenced table.
RELATED_OBJECT_SCHEMA	VARCHAR(128)	The dataset that contains the referenced table.
RELATED_OBJECT	VARCHAR(128)	The name of the table this foreign key references.
RELATED_FIELD	VARCHAR(128)	The name of the column this foreign key references.