If you need values in some of the columns to be unique, you can specify your index as `UNIQUE`.

When a unique index is applied to two or more columns, the combined values in these columns can't be duplicated in multiple rows. Note that because a `NULL` value is treated as a distinct value, you can have multiple `NULL` values in a column with a unique index.

If a table has a primary key defined, a corresponding unique index is created automatically.

The syntax to create a unique index in YCQL is as follows:

```sql
CREATE UNIQUE INDEX index_name ON table_name(column_list);
```

## Example

{{% explore-setup-single-new %}}

1. Create a keyspace and a table as follows:

    ```cql
    ycqlsh> CREATE KEYSPACE yb_demo;
    ycqlsh> USE yb_demo;
    ycqlsh> CREATE TABLE employees(employee_no integer,name text,department text, PRIMARY KEY(employee_no))
            WITH transactions = {'enabled': 'true'};
    ```

1. Create a `UNIQUE` index for the `name` column in the `employees` table to allow only unique names in your table.

    ```cql
    CREATE UNIQUE INDEX index_employee_name ON employees(name);
    ```

1. Use the [DESCRIBE INDEX](../../../../api/ycqlsh/#describe) command to verify the index creation.

    ```cql
    ycqlsh:yb_demo> DESCRIBE INDEX index_employee_name;
    ```

    ```output
    CREATE UNIQUE INDEX index_employee_name ON yb_demo.employees (name) INCLUDE (employee_no)
        WITH transactions = {'enabled': 'true'};
    ```

1. Insert values into the table and verify that no duplicate names are created.

    ```cql
    ycqlsh:yb_demo> INSERT INTO employees(employee_no, name, department) VALUES (1, 'John', 'Sales');
    ycqlsh:yb_demo> INSERT INTO employees(employee_no, name, department) VALUES (2, 'Bob', 'Marketing');
    ycqlsh:yb_demo> INSERT INTO employees(employee_no, name, department) VALUES (3, 'Bob', 'Engineering');
    ```

    ```output
    InvalidRequest: Error from server: code=2200 [Invalid query] message="Execution Error. Duplicate value disallowed by unique index index_employee_name
    INSERT INTO employees(employee_no, name, department) VALUES (3, 'Bob', 'Engineering');
           ^^^^
     (ql error -300)"
    ```

## Learn more

[CREATE INDEX](../../../../api/ycql/ddl_create_index/)