# KEY\_COLUMN\_USAGE

This view contains information about columns that are part of unique keys (constraints) and displays one row per column in a unique constraint.

| Column Name                     | Description                                                                  |
| ------------------------------- | ---------------------------------------------------------------------------- |
| `CONSTRAINT_CATALOG`            | This value is always`def`.                                                   |
| `CONSTRAINT_SCHEMA`             | The name of the related schema (database) for a given key column.            |
| `CONSTRAINT_NAME`               | The name of the related constraint for a given key column.                   |
| `TABLE_CATALOG`                 | Value is always`def`.                                                        |
| `TABLE_SCHEMA`                  | The name of the related schema (database) for a given key column.            |
| `TABLE_NAME`                    | The name of the related table for a given key column.                        |
| `COLUMN_NAME`                   | The name of a given key column.                                              |
| `ORDINAL_POSITION`              | The column’s position within the key. (These are numbered beginning with 1.) |
| `POSITION_IN_UNIQUE_CONSTRAINT` | Always`NULL`.                                                                |
| `REFERENCED_TABLE_SCHEMA`       | Always`NULL`.                                                                |
| `REFERENCED_TABLE_NAME`         | Always`NULL`.                                                                |
| `REFERENCED_COLUMN_NAME`        | Always`NULL`.                                                                |

***

Modified at: August 29, 2022

Source: [/db/v9.1/reference/information-schema-reference/segment-column-and-merge-status/key-column-usage/](https://docs.singlestore.com/db/v9.1/reference/information-schema-reference/segment-column-and-merge-status/key-column-usage/)

(An index of the documentation is available at /llms.txt)