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 37.16. constraint_column_usage Columns
| Column Type Description | 
|---|
| 
        Name of the database that contains the table that contains the column that is used by some constraint (always the current database) | 
| 
        Name of the schema that contains the table that contains the column that is used by some constraint | 
| 
        Name of the table that contains the column that is used by some constraint | 
| 
        Name of the column that is used by some constraint | 
| 
        Name of the database that contains the constraint (always the current database) | 
| 
        Name of the schema that contains the constraint | 
| 
        Name of the constraint |