Cassandra 2.1 数据查询语法。

1,官方文档,基本类型

数据查询语言文档:
http://www.datastax.com/documentation/cql/3.1/cql/cql_reference/update_r.html

cql 支持的数据类型:
相对于 MySQL,有几个类型比较有意思,uuid类型,map,list,set类型,这个优化关联查询,直接将List存入一条记录。

CQL Type Constants Description
ascii strings US-ASCII character string
bigint integers 64-bit signed long
blob blobs Arbitrary bytes (no validation), expressed as hexadecimal
boolean booleans true or false
counter integers Distributed counter value (64-bit long)
decimal integers, floats Variable-precision decimal

Java type

double integers 64-bit IEEE-754 floating point

Java type

float integers, floats 32-bit IEEE-754 floating point

Java type

inet strings IP address string in IPv4 or IPv6 format, used by the python-cql driver and CQL native protocols
int integers 32-bit signed integer
list n/a A collection of one or more ordered elements
map n/a A JSON-style array of literals: { literal : literal, literal : literal ... }
set n/a A collection of one or more elements
text strings UTF-8 encoded string
timestamp integers, strings Date plus time, encoded as 8 bytes since epoch
timeuuid uuids Type 1 UUID only
tuple n/a Cassandra 2.1 and later. A group of 2-3 fields.
uuid uuids A UUID in standard UUID format
varchar strings UTF-8 encoded string
varint integers Arbitrary-precision integer

Java type


java支持的数据类型:

CQL type Java type
decimal java.math.BigDecimal
float java.lang.Float
double java.lang.Double
varint java.math.BigInteger

2,查看,创建keyspace,数据表

查看命令和MySQL类似。
desc cluster;

desc keyspaces;

desc keyspace portfoliodemo;

desc tables;

desc table stocks;
创建keyspace: 默认制定SimpleStrategy的副本类型。
Create a keyspace.
cqlsh> CREATE KEYSPACE demodb WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 } AND durable_writes = true;
Use the keyspace.
cqlsh> USE demodb;
创建数据表:
CREATE TABLE users (
  userid uuid PRIMARY KEY,
  first_name text,
  last_name text,
  emails set,
  top_scores list,
  todo map,
  create_time timestamp
);

Cassandra 有一个特性就是底层做好分布式了,所以再查询排序的时候限制就比较多。
要按照用户才创建时间倒叙查询,必须再创建表的时候就写好。
CREATE TABLE users (
  userid uuid PRIMARY KEY,
  first_name text,
  last_name text,
  emails set,
  top_scores list,
  todo map,
  create_time timestamp
  PRIMARY KEY (userid, create_time)
)
WITH CLUSTERING ORDER BY (create_time DESC);

默认定义的时正序,倒叙需要再定义下,并且把这个字段放入到primary key 里面。
参考:http://www.datastax.com/documentation/cql/3.1/cql/cql_reference/refClstrOrdr.html

更新表结构和mysql类似:
ALTER TABLE users ALTER bio TYPE text;

3,插入数据,更新

和mysq 类似:其中emails是set类型。
INSERT INTO users (userid, first_name, last_name, emails)
  VALUES(cfd66ccc-d857-4e90-b1e5-df98a3d40cd6 , 'Frodo', 'Baggins', {'[email protected]', '[email protected]'});

更新数据,比较特殊的时list,map,set类型:
其他的类似,参考 http://www.datastax.com/documentation/cql/3.1/cql/cql_reference/update_r.html
增加emails数据:使用+
 UPDATE users SET emails = emails + {'[email protected]'} WHERE userid = cfd66ccc-d857-4e90-b1e5-df98a3d40cd6;
删除emails数据:使用-
 UPDATE users SET emails = emails - {'[email protected]'} WHERE userid = cfd66ccc-d857-4e90-b1e5-df98a3d40cd6;
清空emails数据:使用{}
 UPDATE users SET emails = {} WHERE userid = cfd66ccc-d857-4e90-b1e5-df98a3d40cd6;

4,查询数据


查询数量
SELECT COUNT(*) FROM users;
查询前10条
SELECT * FROM users LIMIT 10 ALLOW FILTERING;
按照token查询
SELECT * FROM users WHERE TOKEN(userid) >= TOKEN(cfd66ccc-d857-4e90-b1e5-df98a3d40cd6);
查询token内容,token只能是primary key。
SELECT TOKEN(userid) FROM users WHERE TOKEN(userid) >= TOKEN(cfd66ccc-d857-4e90-b1e5-df98a3d40cd6);

还支持distinct,in等查询,但不支持关联查询,毕竟不是关系型数据库。




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