Cassandra CQL使用详解

Data Types：

cql_type ：：=native_type | collection_type | user_defined_type | tuple_type | custom_type

Native Types：

Counters：

counter type is used to define counter columns. 存储64-bit signed integer 并且支持两种操作 incrementing(增值) and decrementing(减值).

注意计数器的值不能被设置：当counter does not exist until first incremented / decremented，第一次increment / decrement 之前的值是0.

Counters 有几点重要限制：

1）They cannot be used for columns part of the PRIMARY KEY of a table .

2）主键的表的所有列为计数器类型，或者没有一个是计数器类型的.

3）Counters 不支持终止.

4）The delete of counters is supported, but is only guaranteed(担保) to work the first time you delete a counter . 换句话说，你不能重复修改 a counter that you have deleted(if you do , proper behavior is not guaranteed).

5）if a counter update fails unexpectedly(timeout or loss of connection) the client has no way to know if the update has been applied or not , In particular，replaying the update may or may not lead to an over count.

Working with timestamps：

Values of the timestamp type are encode as 64-bit signed integers representing a number of milliseconds since the standard base time known as ：January 1 1970

Timestamps can be input in CQL either using their value as an integer ,or using a string that represents as ISO 8601 date. For instance ,all of the values below：

1299038700000
'2011-02-0304:05+0000'
'2011-02-0304:05:00+0000'
'2011-02-0304:05:00.000+0000'
'2011-02-03T04:05+0000'
'2011-02-03T04:05:00+0000'
'2011-02-03T04:05:00.000+0000'

Working with dates：

Values of the datetype are encoded as 32-bit unsigned integers representing a number of days with “the epoch” atthe center of the range (2^31). Epoch is January 1st, 1970

As for timestamp, a date can be input either as aninteger or using a datestring. In the later case, the format should be yyyy-mm-dd (so'2011-02-03' for instance).

Working with times：

Values of the timetype are encoded as 64-bit signed integers representing the number of nanoseconds since midnight.

As for timestamp, a time can be input either as aninteger or using astringrepresenting the time. In the later case, the format should behh:mm:ss[.fffffffff] (where the sub-second precisionis optional and if provided, can be less than the nanosecond). So for instance, the following are valid inputs for atime:

'08:12:54'
'08:12:54.123'
'08:12:54.123456'
'08:12:54.123456789'

Collections：

CQL supports 3 kind of collections ： Maps Sets Lists

Maps：

A map is a (sorted) set of key-value pairs，where keys are unique and the map is sorted by its keys.