Unique indexes

YSQL
YCQL

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 or a UNIQUE constraint defined, a corresponding UNIQUE index is created automatically.

Syntax

CREATE INDEX index_name ON table_name(column_list);

Example

Follow the steps to create a cluster locally or in YugabyteDB Managed.
Use the YCQL shell for local clusters, or Connect using cloud shell for YugabyteDB Managed, to create a keyspace and a table.

ycqlsh> CREATE KEYSPACE yb_demo;
ycqlsh> USE yb_demo;
ycqlsh> CREATE TABLE employees(employee_no integer,name text,department text, PRIMARY KEY(employee_no));

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

CREATE UNIQUE INDEX index_employee_no ON employees(employee_no);

Use the DESCRIBE INDEX command to verify the index creation.

ycqlsh:yb_demo> DESCRIBE INDEX index_name;

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

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

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');

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

Learn more

For other examples, refer the Create a table with a unique index.