---
title: "Primary keys"
url: "https://docs.yugabyte.com/stable/explore/ycql-language/indexes-constraints/primary-key-ycql/"
---

# Primary keys

Defining Primary key constraint in YCQL

Explore primary keys in YugabyteDB using YCQL

The Primary Key constraint is a means to uniquely identify a specific row in a table via one or more columns. In YCQL, it should be defined either under the `column_constraint` or the `table_constraint`, but not under both:

- **column\_constraint**: Columns can be either STATIC or declared as the PRIMARY KEY. Declaring a column as STATIC results in the same value being shared for all those rows that belong to the same partition (rows with the partition key). Declaring a column as a PRIMARY KEY makes that individual column its sole component.
- **table\_constraint**: PRIMARY KEY defined as the table\_constraint takes columns to form one or more partition keys and zero or more clustering keys. Syntactically, the order is to have the `partition_key_column_list` first, followed by the `clustering_key_column_list`.

Refer to the Grammar section for [CREATE TABLE](/stable/api/ycql/ddl_create_table/#grammar "CREATE TABLE") in YCQL. The [PRIMARY KEY](/stable/api/ycql/ddl_create_table/#primary-key "PRIMARY KEY") section includes details about the [partition key](/stable/api/ycql/ddl_create_table/#partition-key "partition key"), [clustering key](/stable/api/ycql/ddl_create_table/#clustering-key "clustering key"), and [STATIC COLUMNS](/stable/api/ycql/ddl_create_table/#static-columns "STATIC COLUMNS").

## Examples

Before you start

The examples will run on any YugabyteDB universe.  
To create and connect to a universe, see [Set up YugabyteDB universe](/stable/explore/cluster-setup-local/).

### Column constraint

1. Create a `users` table with `user_id` as the primary key.
   
   ```cql
   CREATE TABLE users(user_id INT PRIMARY KEY, full_name TEXT);
   ```
2. Insert two rows into the table and check the entries.
   
   ```cql
   INSERT INTO users(user_id , full_name) VALUES (1, 'John');
   INSERT INTO users(user_id , full_name) VALUES (1, 'Rose');
   SELECT * FROM users;
   ```
   
   ```output
    user_id | full_name
   ---------+-----------
          1 |       Rose
   ```

The second entry with `Rose` as the `full_name` overrides the first entry because the `user_id` is the same.

### Table constraint

1. Create a `devices` table with `supplier_id` and `device_id` as the partitioning columns and `model` year as the clustering column.
   
   ```cql
   CREATE TABLE devices(supplier_id INT,
                       device_id INT,
                       model_year INT,
                       device_name TEXT,
                       PRIMARY KEY((supplier_id, device_id), model_year));
   ```
2. Insert three rows into the table and view the contents.
   
   ```cql
   INSERT INTO devices(supplier_id, device_id, device_name, model_year) VALUES (1, 101, 'iPhone', 2013);
   INSERT INTO devices(supplier_id, device_id, device_name, model_year) VALUES (1, 102, 'Pixel', 2011);
   INSERT INTO devices(supplier_id, device_id, device_name, model_year) VALUES (1, 102, 'Samsung S3', 2001);
   SELECT * FROM devices;
   ```
   
   ```output
    supplier_id | device_id | model_year | device_name
   -------------+-----------+------------+-------------
              1 |       101 |       2013 |      iPhone
              1 |       102 |       2001 |     Samsung
              1 |       102 |       2011 |       Pixel
   
   (3 rows)
   ```
3. Insert another entry with `supplier_id`, `device_id`, and `model_year` as 1, 102, and 2011 respectively.
   
   ```cql
   INSERT INTO devices(supplier_id, device_id, device_name, model_year) VALUES (1, 102, 'MotoRazr', 2011);
   SELECT * FROM devices;
   ```
   
   ```output
    supplier_id | device_id | model_year | device_name
   -------------+-----------+------------+-------------
              1 |       101 |       2013 |      iPhone
              1 |       102 |       2001 |     Samsung
              1 |       102 |       2011 |    MotoRazr
   ```

The row with `device_name` Pixel is replaced with MotoRazr.

## Explore more examples

- [Use column constraint to define a static column](/stable/api/ycql/ddl_create_table/#use-column-constraint-to-define-a-static-column "Use column constraint to define a static column")
- [Example for clustering columns by ORDER](/stable/api/ycql/ddl_create_table/#use-table-property-to-define-the-order-ascending-or-descending-for-clustering-columns "Example for clustering columns by ORDER")
- [Example to define the default expiration time for rows](/stable/api/ycql/ddl_create_table/#use-table-property-to-define-the-default-expiration-time-for-rows "Example to define the default expiration time for rows")
- [Create a table specifying the number of tablets](/stable/api/ycql/ddl_create_table/#create-a-table-specifying-the-number-of-tablets "Create a table specifying the number of tablets")