Cassandra CQL user-defined data types

CQL provides the ibility to create and use user-defined data types. Y ou can create a data type to handle multiple fields. This chapter describes how to create, change, and delete user-defined data types.

Create a user-defined data type

The command CREATE TYPE is used to create user-defined data types. The syntax is as follows:

CREATE TYPE <keyspace name>. <data typename>
( variable1, variable2).

Example

Here's an example of creating a user-defined data type. In this example, we are creating a data type that contains card_details following details.

cqlsh:tutorialspoint> CREATE TYPE card_details (
   ... num int,
   ... pin int,
   ... name text,
   ... cvv int,
   ... phone set<int>
... );

Note: The name used for user-defined data types should not match the reserved type name.

Verify

Use the DESCRIBE command to verify that the created type has been created.

CREATE TYPE tutorialspoint.card_details (
   num int,
   pin int,
   name text,
   cvv int,
   phone set<int>
   );

Change the user-defined data type

The ALTER TYPE command is used to change an existing data type. With ALTER, you can add new fields or rename existing fields.

Add a field to the type

Use the following syntax to add new fields to existing user-defined data types.

ALTER TYPE typename
ADD field_name field_type; 

The following code Card_details a new field to the data type. Here we add a new field called email.

cqlsh:tutorialspoint> ALTER TYPE card_details ADD email text;

Verify

Use the DESCRIBE command to verify that a new field is added.

cqlsh:tutorialspoint> describe type card_details;
CREATE TYPE tutorialspoint.card_details (
   num int,
   pin int,
   name text,
   cvv int,
   phone set<int>,
   );

Rename the field in the type

Rename an existing user-defined data type using the following syntax.

ALTER TYPE typename
RENAME existing_name TO new_name;

The following code changes the name of the field in the type. Here we rename the field email to mail.

cqlsh:tutorialspoint> ALTER TYPE card_details RENAME email TO mail;

Verify

Use the DESCRIBE command to verify that the type name has changed.

cqlsh:tutorialspoint> describe type card_details;
CREATE TYPE tutorialspoint.card_details (
   num int,
   pin int,
   name text,
   cvv int,
   phone set<int>,
   mail text
   );

Delete user-defined data types

DROP TYPE is a command that removes user-defined data types. Here's an example of deleting a user-defined data type.

Example

Before deleting, use the DESCRIBE_TYPES command to verify a list of all user-defined data types, as shown below.

cqlsh:tutorialspoint> DESCRIBE TYPES;
card_details card

From both types, remove the type named card, as shown below.

cqlsh:tutorialspoint> drop type card;

Use the DESCRIBE command to verify that the data type is missing.

cqlsh:tutorialspoint> describe types;

card_details