How to Create a Primary Key in Cassandra?

You can't explicitly create a primary key in Cassandra like you might in other databases. Instead, you define it when creating your table. Here's how:

Define the Primary Key in the CREATE TABLE Statement:

When you create a table, you specify the primary key as part of the table definition. This is done using the PRIMARY KEY clause.

Example:
```
CREATE TABLE users (
    user_id uuid PRIMARY KEY,
    username text,
    email text
);
```
In this example, user_id is the primary key.
Composite Primary Keys:

Cassandra supports composite primary keys, which consist of multiple columns. You need to define the clustering columns within the PRIMARY KEY clause.

Example:
```
CREATE TABLE orders (
    customer_id uuid,
    order_date timestamp,
    order_id int,
    product_name text,
    PRIMARY KEY (customer_id, order_date, order_id)
);
```
Here, the primary key is composed of customer_id, order_date, and order_id. customer_id is the partition key, and order_date and order_id are the clustering columns.

Key Points:

Partition Key: The first column in a composite primary key is the partition key. It determines which node in the Cassandra cluster will store the data.
Clustering Columns: The remaining columns in a composite primary key are clustering columns. They define the order of data within a partition.
Data Consistency: Cassandra guarantees that data within a partition is consistent.

Practical Insights:

Choosing the Right Primary Key: Carefully consider the access patterns and querying needs of your application when designing your primary key.
Performance Optimization: A well-designed primary key can significantly improve query performance.

Remember: Cassandra doesn't allow you to modify the primary key of a table after it's been created. You'll need to create a new table with the desired primary key structure and migrate your data.

A2oz

How to Create a Primary Key in Cassandra?

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