The SYS_TABLE_CONSTRAINTS table lists constraints and specifies their types and tables they belong to. Each collection has one constraint, its primary key on _id; views have none. Unique indexes are listed in SYS_INDEXES. It has the following columns:

Column Name	Data Type	Description
CONSTRAINT_CATALOG	VARCHAR	The name of the database of the connection.
CONSTRAINT_SCHEMA	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
CONSTRAINT_NAME	VARCHAR	The name of the constraint: PK_ followed by the name of the collection, for example PK_customers.
TABLE_CATALOG	VARCHAR	The name of the database of the connection.
TABLE_SCHEMA	VARCHAR	Not used in dotConnect for MongoDB. Always NULL.
TABLE_NAME	VARCHAR	The name of the collection which the constraint belongs to.
CONSTRAINT_TYPE	VARCHAR	Type of a constraint. Always "PRIMARY KEY".
IS_DEFERRABLE	VARCHAR	Not used in dotConnect for MongoDB. Always "NO".
INITIALLY_DEFERRED	VARCHAR	Not used in dotConnect for MongoDB. Always "NO".