How to change the primary key in Cassandra?

@verlie.homenick 

In Cassandra, the primary key is defined when you create a table. It consists of one or more columns that uniquely identify each row in the table. If you want to change the primary key of an existing table, you can do so using the following steps:

1. Create a new table with the desired primary key. You can do this using the CREATE TABLE statement.
2. Insert the data from the original table into the new table. You can do this using the INSERT INTO statement.
3. Drop the original table. You can do this using the DROP TABLE statement.
4. Rename the new table to the name of the original table. You can do this using the ALTER TABLE statement.

For example, suppose you have a table users with the following schema:

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CREATE TABLE users (
  user_id int PRIMARY KEY,
  name text,
  email text
);

To change the primary key to email, you can create a new table as follows:

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CREATE TABLE new_users (
  email text PRIMARY KEY,
  name text,
  user_id int
);

Then, you can insert the data from the users table into the new_users table using the following statement:

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INSERT INTO new_users (email, name, user_id) SELECT email, name, user_id FROM users;

Finally, you can drop the users table and rename the new_users table to users using the following statements:

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DROP TABLE users;
ALTER TABLE new_users RENAME TO users;

It's important to note that changing the primary key of a table in Cassandra can be a time-consuming operation, especially if the table is large. It's also worth considering whether changing the primary key is necessary, as it can potentially impact application code that depends on the original primary key.