The SYS_REFERENTIAL_CONSTRAINTS table is meant for the details of foreign keys. MongoDB has no foreign keys, so the table is always empty; it is kept for the compatibility of the information schema. It has the following columns:

Column Name	Data Type	Description
CONSTRAINT_CATALOG	VARCHAR	Top-level container for constraints.
CONSTRAINT_SCHEMA	VARCHAR	Second-level container for constraints.
CONSTRAINT_NAME	VARCHAR	The name of the foreign key constraint.
UNIQUE_CONSTRAINT_CATALOG	VARCHAR	Top-level container for referenced constraints.
UNIQUE_CONSTRAINT_SCHEMA	VARCHAR	Second-level container for referenced constraints.
UNIQUE_CONSTRAINT_NAME	VARCHAR	The name of the referenced constraint.
MATCH_OPTION	VARCHAR	The match option of the constraint.
UPDATE_RULE	VARCHAR	Action to perform when an UPDATE violates the constraint.
DELETE_RULE	VARCHAR	Action to perform when a DELETE violates the constraint.
OBJECT_CATALOG	VARCHAR	Top-level container of the table this foreign key belongs to.
OBJECT_SCHEMA	VARCHAR	Second-level container of the table this foreign key belongs to.
OBJECT	VARCHAR	The name of the table this foreign key belongs to.
FIELD	VARCHAR	The foreign key column.
RELATED_OBJECT_CATALOG	VARCHAR	Top-level container of the table this foreign key references.
RELATED_OBJECT_SCHEMA	VARCHAR	Second-level container of the table this foreign key references.
RELATED_OBJECT	VARCHAR	The name of the table this foreign key references.
RELATED_FIELD	VARCHAR	The name of the column this foreign key references.