demo如下：
CREATE TABLE users3 ( user_id text PRIMARY KEY, first_name text, last_name text, emails list<text> ); INSERT INTO users3 (user_id, first_name, last_name, emails) VALUES(‘frodo‘, ‘Frodo‘, ‘Baggins‘, [‘[email protected]‘, ‘[email protected]‘]); UPDATE users3 SET emails = emails + [‘[email protected]‘] WHERE user_id = ‘frodo‘; SELECT user_id, emails FROM users3 WHERE user_id = ‘frodo‘;
Collection type
A collection column is declared using the collection type, followed by another type, such as int or text, in angle brackets. For example, you can create a table having a list of textual elements, a list of integers, or a list of some other element types.
list<text>
list<int>Collection types cannot be nested, but frozen collection types can be nested inside frozen or non-frozen collections. For example, you may define a list within a list, provided the inner list is frozen:
list<frozen <list<int>>>Indexes may be created on a collection column of any type.
Using frozen in a collection
A frozen value serializes multiple components into a single value. Non-frozen types allow updates to individual fields. Cassandra treats the value of a frozen type as a blob. The entire value must be overwritten.
column_name collection_type<data_type, frozen<column_name>>For example:
CREATE TABLE mykeyspace.users (
id uuid PRIMARY KEY,
name frozen <fullname>,
direct_reports set<frozen <fullname>>, // a collection set
addresses map<text, frozen <address>> // a collection map
score set<frozen <set<int>>> // a set with a nested frozen set
);
list的话针对下面的{}修改为[]即可！Using the set type
A set stores a group of elements that are returned in sorted order when queried. A column of type set consists of unordered unique values. Using the set data type, you can solve the multiple email problem in an intuitive way that does not require a read before adding a new email address.
Procedure
- Define a set, emails, in the users table to accommodate multiple email address.
CREATE TABLE users ( user_id text PRIMARY KEY, first_name text, last_name text, emails set<text> );
- Insert data into the set, enclosing values in curly brackets.
Set values must be unique.INSERT INTO users (user_id, first_name, last_name, emails) VALUES(‘frodo‘, ‘Frodo‘, ‘Baggins‘, {‘[email protected]‘, ‘[email protected]‘}); - Add an element to a set using the UPDATE command and the addition (+) operator.
UPDATE users SET emails = emails + {‘[email protected]‘} WHERE user_id = ‘frodo‘; - Retrieve email addresses for frodo from the set.
SELECT user_id, emails FROM users WHERE user_id = ‘frodo‘;
When you query a table containing a collection, Cassandra retrieves the collection in its entirety; consequently, keep collections small enough to be manageable, or construct a data model to replace collections that can accommodate large amounts of data.
Cassandra returns results in an order based on the type of the elements in the collection. For example, a set of text elements is returned in alphabetical order. If you want elements of the collection returned in insertion order, use a list.
user_id | emails ---------+------------------------------------------------------------------- frodo | {"[email protected]","[email protected]","[email protected]"} - Remove an element from a set using the subtraction (-) operator.
UPDATE users SET emails = emails - {‘[email protected]‘} WHERE user_id = ‘frodo‘; - Remove all elements from a set by using the UPDATE or DELETE statement.
A set, list, or map needs to have at least one element; otherwise, Cassandra cannot distinguish the set from a null value.UPDATE users SET emails = {} WHERE user_id = ‘frodo‘; DELETE emails FROM users WHERE user_id = ‘frodo‘;A query for the emails returns null.
SELECT user_id, emails FROM users WHERE user_id = ‘frodo‘;
user_id | emails ---------+------------------------------------------------ frodo | null 参考:http://docs.datastax.com/en/archived/cql/3.0/cql/cql_using/use_list_t.html