Cassandra Data Types | CQL Data Types

What Is CQL?

Cassandra Query Language (CQL) is a query language that is used with theCassandra datatypes. This version of CQL is compatible with Cassandra 3.x. The primary language for connecting with the Cassandra database is the Cassandra Query Language (CQL). The CQL shell, cqlsh, is the simplest fundamental way to interface with Cassandra. You may use cqlsh to construct keyspaces and tables, insert and query tables, and much more.

Cassandra Data types

Data types often denote the type of variables used in a program. Many data types have been examined in different programming languages. For example, int, char, float, and so on. There are several data kinds in the Cassandra query language.

Built-in, collection, and user-defined data types are among the Cassandra datatypes. The user can select any of these based on the program's requirements.

Built-in Type

CQL has a large number of native data types. These data types are predefined, and we may refer to any of them directly.

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Collection Data types

We may need to store data of the same type without creating additional columns. Multiple values can be stored in a collection data type. CQL gives us three collection types to assist us: lists, sets, and maps. We may, for example, establish a table with a list of textual items, a list of numbers, or a list of other element kinds.

CQL recognizes three types of collections: maps, sets, and lists. The categories of those collections are specified as follows:

collection_type::= MAP '<' cql_type',' cql_type'>'

| SET '<' cql_type '>'

| LIST '<' cql_type'>'

Collection literals can be used to enter their values:

collection_literal::= map_literal | set_literal | list_literal

map_literal::= '\{' [ term ':' term (',' term : term)* ] '}'

set_literal::= '\{' [ term (',' term)* ] '}'

list_literal::= '[' [ term (',' term)* ] ']'

Set

Using the set data type, we can store several unique values. Similarly, items are not saved in order in Java. Let's make a set:

CREATE TABLE collection_types

(

    primaryKey int PRIMARY KEY,

    email set<text>

);

List

The values of this data type are kept in the form of a list. We are unable to adjust the order of the items. After saving the data in the list, each element is assigned an index. Using these indices, we may obtain data.

Lists, unlike sets, may hold duplicate values. Let us add the following to our table:

ALTER TABLE collection_types

    ADD scores list<text>;

Map

We can use Cassandra's map data type to store data in sets of key-value pairs. Keys are one-of-a-kind items. As a result, we can order maps based on their keys.

Let us now add a new column to our table:

ALTER TABLE collection_types

    ADD address map<uuid, text>;

Using Frozen in a Collection

Multiple components are serialized into a single value by a frozen value. Individual fields can be updated in non-frozen kinds. Cassandra datatypes consider the value of a frozen type to be a blob. Overwriting the full value is required.

column_name collection_type<data_type, frozen<column_name>>

Let’s take an example:

CREATE TABLE mykeyspace.users (

  id uuid PRIMARY KEY,

  name frozen <fullname>,

  direct_reports set<frozen <fullname>>,    

  addresses map<text, frozen <address>>     

  score set<frozen <set<int>>>             

);

Other Data types

1. A boolean value is just a true/false value.
2. uuid is a Type 4 UUID that is solely based on random digits. UUIDs can be entered using dash-separated hex digit sequences.
3. A binary big object (blob) is a slang word for an arbitrary array of bytes in computing. CQL blobs are used to hold media or other binary file formats. The blob size limit is 2 GB, however less than 1 MB is preferred.
4. The inet type represents IPv4 or IPv6 Internet addresses.

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User-Defined Datatypes

Cqlsh gives users the option of building their own data types. An example of a user-defined data type is shown below. In this example, we'll build a card details data type with the following information.

CREATE TYPE card_details (

... num int,

... pin int,

... name text,

... cvv int,

... phone set<int>

... );

The commands used when working with user-defined data types are listed below.

1. CREATE TYPE: creates a custom datatype.

2. DROP TYPE: is used to remove a user-defined datatype.

Example

Let’s see how to delete the type named card. Use the syntax written below:

drop type card;

3. ALTER TYPE: is used to modify a user-defined datatype.

To add a new field to an existing user-defined data type, use the syntax below.

ALTER TYPE typename

ADD field_name field_type;

The code that follows adds a new field to the Card details data type. We're going to add a new field named email here.

ALTER TYPE card_details ADD email text;

4. DESCRIBE TYPE: Describes a data type that has been specified by the user.

5. DESCRIBE TYPES: Describes datatypes that have been specified by the user.

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