The KEY_COLUMN_USAGE rowset identifies the columns defined in the catalog that are constrained as keys by a given user.
The KEY_COLUMN_USAGE rowset contains the following columns.
| Column name | Type indicator | Description |
| CONSTRAINT_CATALOG | DBTYPE_WSTR | Catalog name. NULL if the provider does not support catalogs. |
| CONSTRAINT_SCHEMA | DBTYPE_WSTR | Unqualified schema name. NULL if the provider does not support schemas. |
| CONSTRAINT_NAME | DBTYPE_WSTR | Constraint name. |
| TABLE_CATALOG | DBTYPE_WSTR | Catalog name in which the table containing the key column is defined. NULL if the provider does not support catalogs. |
| TABLE_SCHEMA | DBTYPE_WSTR | Unqualified schema name in which the table containing the key column is defined. NULL if the provider does not support schemas. |
| TABLE_NAME | DBTYPE_WSTR | Table name containing the key column. |
| COLUMN_NAME | DBTYPE_WSTR | Name of the column participating in the unique, primary, or foreign key. This column, together with the COLUMN_GUID and COLUMN_PROPID columns, forms the column ID. One or more of these columns will be NULL depending on which elements of the DBID structure the provider uses. |
| COLUMN_GUID | DBTYPE_GUID | Column GUID. |
| COLUMN_PROPID | DBTYPE_UI4 | Column property ID. |
| ORDINAL_POSITION | DBTYPE_UI4 | Ordinal position of the column in the constraint being described. If the constraint being described is a key of cardinality one, the value of ORDINAL_POSITION is always one. |
Default Sort Order: CONSTRAINT_CATALOG, CONSTRAINT_SCHEMA, CONSTRAINT_NAME, TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME, ORDINAL_POSITION