35.9. 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  |