Create a collection

To create a collection, you must define the collection type, column name, and column data type. The cqlsh command-line tool is the primary tool for interacting with CQL to define schema.

Make sure you understand the differences in the collection types before creating a collection, as well as the difference between frozen and non-frozen collections.

Collections are not paged internally. Reading a range of values is not supported for collections.

Prerequisites

  • Keyspace must exist.

  • Understand the use and importance of the primary key in table schema.

  • Determine the type of collection you want to create.

Set collections

A set consists of a unordered group of elements with unique values. Duplicate values will not be stored distinctly. The values of a set are stored unordered, but will return the elements in sorted order when queried. Use the set data type to store data that has a many-to-one relationship with another column.

Non-frozen set

To create a non-frozen set collection in a table, specify the collection column name and column data type enclosed in angle brackets:

CREATE TABLE IF NOT EXISTS cycling.cyclist_career_teams (
  id UUID PRIMARY KEY,
  lastname text,
  teams set<text>
);
Results

The set collection is created with the column name teams, and the data type text.

Frozen set

To create a frozen set collection in a table specify the collection column name and a column data type enclosed with angle brackets, with the FROZEN keyword:

CREATE TABLE IF NOT EXISTS cycling.race_results (
  race_name text PRIMARY KEY, 
  race_history frozen<set<int>>,
  top_three frozen<map<int, text>>
);
Results

The set collection is created with the column name race_history, and the data type int.

CREATE TABLE cycling.race_results (
    race_name text PRIMARY KEY,
    race_history frozen<set<int>>,
    top_three frozen<map<int, text>>
) WITH additional_write_policy = '99PERCENTILE'
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND nodesync = {'enabled': 'true', 'incremental': 'true'}
    AND read_repair = 'BLOCKING'
    AND speculative_retry = '99PERCENTILE';

List collections

A list is similar to a set; it groups and stores values. Unlike a set, the values stored in a list do not need to be unique and can be duplicated. In addition, a list stores the elements in a particular order and may be inserted or retrieved according to an index value.

Use the list data type to store data that has a possible many-to-many relationship with another column.

Non-frozen list

To create a non-frozen list collection in a table, specify a collection column name, and a column data type enclosed in angle brackets:

CREATE TABLE IF NOT EXISTS cycling.upcoming_calendar (
  year int,
  month int,
  events list<text>,
  PRIMARY KEY (year, month)
);
Results

The list collection is created with the column name events, and the data type text.

CREATE TABLE cycling.upcoming_calendar (
    year int,
    month int,
    events list<text>,
    PRIMARY KEY (year, month)
) WITH CLUSTERING ORDER BY (month ASC)
    AND additional_write_policy = '99PERCENTILE'
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND nodesync = {'enabled': 'true', 'incremental': 'true'}
    AND read_repair = 'BLOCKING'
    AND speculative_retry = '99PERCENTILE';

Frozen list

To create a frozen list collection in a table, specify a collection column name and a column data type enclosed in angle brackets, with the FROZEN keyword:

CREATE TABLE IF NOT EXISTS cycling.race_starts (
  cyclist_name text PRIMARY KEY,
  rnumbers FROZEN<LIST<int>>
);
Results

The list collection is created with the column name rnumbers, and the data type int.

CREATE TABLE cycling.race_starts (
    cyclist_name text PRIMARY KEY,
    rnumbers frozen<list<int>>
) WITH additional_write_policy = '99PERCENTILE'
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND nodesync = {'enabled': 'true', 'incremental': 'true'}
    AND read_repair = 'BLOCKING'
    AND speculative_retry = '99PERCENTILE';

Map collections

A map relates one item to another with a key-value pair. For each key, only one value may exist, and duplicates cannot be stored. Both the key and the value are designated with a data type.

For example, using the map type, you can store timestamp-related information in user profiles. Each element of a non-frozen map is internally stored as a single column that you can modify, replace, delete, and query. Each element can have an individual time-to-live and expire when the TTL ends.

Non-frozen map

To create a non-frozen map collection in a table, specify a collection column name, and a pair of column data types enclosed in angle brackets:

CREATE TABLE IF NOT EXISTS cycling.cyclist_teams (
  id uuid PRIMARY KEY,
  firstname text,
  lastname text,
  teams map<int, text>
);
Results

The map collection is created with the column name teams, and the data types will have a key year of integer type, and a team name value of text type.

CREATE TABLE cycling.cyclist_teams (
    id uuid PRIMARY KEY,
    firstname text,
    lastname text,
    teams map<int, text>
) WITH additional_write_policy = '99PERCENTILE'
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND nodesync = {'enabled': 'true', 'incremental': 'true'}
    AND read_repair = 'BLOCKING'
    AND speculative_retry = '99PERCENTILE';

Frozen map

To create a frozen map collection in a table, specify a collection column name, and a pair of column data types enclosed in angle brackets, with the FROZEN keyword:

CREATE TABLE IF NOT EXISTS cycling.race_results (
  race_name text PRIMARY KEY, 
  race_history frozen<set<int>>,
  top_three frozen<map<int, text>>
);
Results

The map collection is created with the column name top_three, and the data types will have a key rank of integer type, and a cyclist name value of text type.

CREATE TABLE cycling.race_results (
    race_name text PRIMARY KEY,
    race_history frozen<set<int>>,
    top_three frozen<map<int, text>>
) WITH additional_write_policy = '99PERCENTILE'
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND nodesync = {'enabled': 'true', 'incremental': 'true'}
    AND read_repair = 'BLOCKING'
    AND speculative_retry = '99PERCENTILE';

Related information:

CREATE TABLE, ALTER TABLE, Collection types

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