check_constraints #
   The view check_constraints contains all check
   constraints, either defined on a table or on a domain, that are
   owned by a currently enabled role.  (The owner of the table or
   domain is the owner of the constraint.)
  
   The SQL standard considers not-null constraints to be check constraints
   with a CHECK ( expression.  So not-null constraints are also included here
   and don't have a separate view.
  column_name IS NOT
   NULL)
Table 35.7. check_constraints Columns
| Column Type Description | 
|---|
| 
        Name of the database containing the constraint (always the current database) | 
| 
        Name of the schema containing the constraint | 
| 
        Name of the constraint | 
| 
        The check expression of the check constraint |