key_column_usage
key_column_usage identifies all columns that are restricted by some unique, primary key, or foreign key constraint.
The following fields are provided in key_column_usage:
| Field | Description |
|---|---|
| CONSTRAINT_CATALOG | The name of the catalog to which the constraint belongs. This value is always def. |
| CONSTRAINT_SCHEMA | The name of the database to which the constraint belongs. |
| CONSTRAINT_NAME | The name of the constraint. |
| TABLE_CATALOG | The name of the catalog to which the table belongs. This value is always def. |
| TABLE_SCHEMA | The name of the database to which the table belongs. |
| TABLE_NAME | The name of the table that has the constraint. |
| COLUMN_NAME | The name of the column that has the constraint.If the constraint is a foreign key, then this is the column of the foreign key, not the column that the foreign key references. |
| ORDINAL_POSITION | The column's position within the constraint, not the column's position within the table. Column positions are numbered beginning with 1. |
| POSITION_IN_UNIQUE_CONSTRAINT | NULL for unique and primary-key constraints. For foreign-key constraints, this column is the ordinal position in key of the table that is being referenced. |
| REFERENCED_TABLE_SCHEMA | The name of the schema referenced by the constraint. |
| REFERENCED_TABLE_NAME | The name of the table referenced by the constraint. |
| REFERENCED_COLUMN_NAME | The name of the column referenced by the constraint. |