Cassandra集合用於處理任務。 您可以在集合中儲存多個元素。 Cassandra支援三種型別的集合：
Set集合儲存查詢時返回排序元素的元素組。
語法：
Create table table_name
(
id int,
Name text,
Email set<text>,
Primary key(id)
);
範例：
下面舉個例子來展示Set集合。建立一個具有三列(id, name 和 email)的表「employee」。
use yiibai_ks;
create table employee(
id int,
name text,
email set<text>,
primary key(id)
);
執行上面語句建立表以後如下：
cqlsh:yiibai_ks> create table employee(
... id int,
... name text,
... email set<text>,
... primary key(id)
... );
cqlsh:yiibai_ks> describe employee;
CREATE TABLE yiibai_ks.employee (
id int PRIMARY KEY,
email set<text>,
name text
) WITH 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 dclocal_read_repair_chance = 0.1
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 read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';
cqlsh:yiibai_ks>
現在，向上面建立的employee表中插入一些值：
INSERT INTO employee (id, email, name)
VALUES(1, {'[email protected]'}, 'yestouu');
INSERT INTO employee (id, email, name)
VALUES(2,{'[email protected]'}, 'Kanchan');
INSERT INTO employee (id, email, name)
VALUES(3, {'[email protected]'}, 'Maxsu');
執行上面語句結果如下 -
cqlsh:yiibai_ks> INSERT INTO employee (id, email, name)
... VALUES(1, {'[email protected]'}, 'yestouu');
cqlsh:yiibai_ks> INSERT INTO employee (id, email, name)
... VALUES(2,{'[email protected]'}, 'Kanchan');
cqlsh:yiibai_ks> INSERT INTO employee (id, email, name)
... VALUES(3, {'[email protected]'}, 'Maxsu');
cqlsh:yiibai_ks> select * from employee;
id | email | name
----+-----------------------+---------
1 | {'[email protected]'} | yestouu
2 | {'[email protected]'} | Kanchan
3 | {'[email protected]'} | Maxsu
(3 rows)
cqlsh:yiibai_ks>
當元素的順序重要時，使用列表(List)集合。我們以擴充套件上面範例中的employee表並新增一列department為例。
alter table employee add department list<text>;
執行結果如下 -
cqlsh:yiibai_ks> alter table employee add department list<text>;
cqlsh:yiibai_ks> select * from employee;
id | department | email | name
----+------------+-----------------------+---------
1 | null | {'[email protected]'} | yestouu
2 | null | {'[email protected]'} | Kanchan
3 | null | {'[email protected]'} | Maxsu
(3 rows)
cqlsh:yiibai_ks>
現在新增新列(department)。 在新列「department」中插入一些值。
INSERT INTO employee (id, email, name, department) VALUES(4, {'[email protected]'}, 'Sweetsu', ['IT Devopment']);
執行上面語句結果如下 -
cqlsh:yiibai_ks> alter table employee add department list<text>;
cqlsh:yiibai_ks> select * from employee;
id | department | email | name
----+------------+-----------------------+---------
1 | null | {'[email protected]'} | yestouu
2 | null | {'[email protected]'} | Kanchan
3 | null | {'[email protected]'} | Maxsu
(3 rows)
cqlsh:yiibai_ks> INSERT INTO employee (id, email, name, department) VALUES(4, {'[email protected]'}, 'Sweetsu', ['IT Devopment']);
cqlsh:yiibai_ks> select * from employee;
id | department | email | name
----+------------------+-----------------------+---------
1 | null | {'[email protected]'} | yestouu
2 | null | {'[email protected]'} | Kanchan
4 | ['IT Devopment'] | {'[email protected]'} | Sweetsu
3 | null | {'[email protected]'} | Maxsu
(4 rows)
cqlsh:yiibai_ks>
Map集合用於儲存鍵值對。它將一件事對映到另一件事。 例如，如果要將必備課程名稱來儲存課程資訊，則可以使用Map集合。
例子：
建立一個名為「course」的表。
create table course(
id int,
prereq map<text, text>,
primary key(id)
);
-- 插入資料
INSERT into course(id,prereq) VALUES(1, {'Programming':'CPP&&Java', 'Network':'Artificail Intelligence'});
現在建立表，在Map集合型別中插入一些資料。
輸出：
cqlsh:yiibai_ks> create table course(
... id int,
... prereq map<text, text>,
... primary key(id)
... );
cqlsh:yiibai_ks> INSERT into course(id,prereq) VALUES(1, {'Programming':'CPP&&Java', 'Network':'Artificail Intelligence'});
cqlsh:yiibai_ks> select * from course;
id | prereq
----+--------------------------------------------------------------------
1 | {'Network': 'Artificail Intelligence', 'Programming': 'CPP&&Java'}
(1 rows)
cqlsh:yiibai_ks>