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

In this topic:

• Blob type
  
• Collection type
  
• Counter type
  
• UUID and timeuuid types
  
• uuid and Timeuuid functions
  
• Timestamp type
  
• Tuple type
  
• User-defined type

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。