35.18. 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 not-null constraint, this view identifies the column that the constraint is defined on. 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 35.16. 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  |