constraint_table_usage
   The view constraint_table_usage identifies all
   tables in the current database that are used by some constraint and
   are owned by a currently enabled role.  (This is different from the
   view table_constraints, which identifies all
   table constraints along with the table they are defined on.)  For a
   foreign key constraint, this view identifies the table that the
   foreign key references.  For a unique or primary key constraint,
   this view simply identifies the table the constraint belongs to.
   Check constraints and not-null constraints are not included in this
   view.
  
Table 36.17. constraint_table_usage Columns
| Name | Data Type | Description | 
|---|---|---|
| table_catalog | sql_identifier | Name of the database that contains the table that is used by some constraint (always the current database) | 
| table_schema | sql_identifier | Name of the schema that contains the table that is used by some constraint | 
| table_name | sql_identifier | Name of the table that is used by some constraint | 
| constraint_catalog | sql_identifier | Name of the database that contains the constraint (always the current database) | 
| constraint_schema | sql_identifier | Name of the schema that contains the constraint | 
| constraint_name | sql_identifier | Name of the constraint |