36.18. constraint_column_usage
  The view
  
   constraint_column_usage
  
  identifies all
   columns in the current database that are used by some constraint.
   Only those columns are shown that are contained in a table owned by
   a currently enabled role.  For a check constraint, this view
   identifies the columns that are used in the check expression.  For
   a foreign key constraint, this view identifies the columns that the
   foreign key references.  For a unique or primary key constraint,
   this view identifies the constrained columns.
 
   
    Table 36.16. 
    
     constraint_column_usage
    
    Columns
   
  
| Name | Data Type | Description | 
|---|---|---|
| 
        table_catalog
        | 
        sql_identifier
        | Name of the database that contains the table that contains the column that is used by some constraint (always the current database) | 
| 
        table_schema
        | 
        sql_identifier
        | Name of the schema that contains the table that contains the column that is used by some constraint | 
| 
        table_name
        | 
        sql_identifier
        | Name of the table that contains the column that is used by some constraint | 
| 
        column_name
        | 
        sql_identifier
        | Name of the column 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 |