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
   the current user.  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 31-8. 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 |