问题描述
在 cassandra 中创建表时，我们可以按如下顺序给出聚类键.
When creating table in cassandra, we can give clustering keys with ordering like below.
Create table user(partitionkey int, id int, name varchar, age int, address text,
insrt_ts timestamp,
Primary key(partitionkey, name, insrt_ts, id)
with clustering order by (name asc, insrt_ts desc, id asc);
当我们将数据插入到该表中时，根据 cassandra 文档记录根据聚类键进行排序.
when we insert data into that table, As per cassandra documentation records are sorted based on clustering keys.
当我使用 CQL1 和 CQL2 检索记录时，我的排序顺序相同.
When i retrieve records with CQL1 and CQL2, I am getting in the same sorted order.
CQL1:
Select * from user where partitionkey=101;
CQL2:
Select * from user where partitionkey=101 order by name, insrt desc, id;
CQL1 和 CQL2 有什么区别?
what is the difference between CQL1 and CQL2?
推荐答案
DataStax 推荐了一种面向查询的数据建模方法，其中结果按照查询时所需的顺序存储.此顺序由 [复合] 主键的分区键和第一个集群列确定. 上的 DataStax 文档ORDER BY 子句 解释了这一点:
DataStax recommends a query-oriented data modeling approach, where the results are stored in the order in which they are required at query-time. This order is determined by both the partition key and first clustering column of a [compound] primary key. The DataStax doc on the ORDER BY clause explains this:
查询复合主键和排序结果 ORDER BY 子句只能选择单列.该列必须是第二个复合 PRIMARY KEY 中的列.这也适用于带有主键中有两个以上的列组件.订购可以按升序或降序完成，默认升序，以及使用 ASC 或 DESC 关键字指定.
在 ORDER BY 子句中，参考到使用实际名称的列，而不是别名.
In the ORDER BY clause, refer to a column using the actual name, not the aliases.
例如设置在使用复合主键的播放列表表中插入示例数据，并使用此查询获取有关特定数据的信息播放列表，按song_order 排序.从 Cassandra 1.2 开始，您不需要在选择表达式中包含 ORDER BY 列.
For example, set up the playlists table, which uses a compound primary key, insert the example data, and use this query to get information about a particular playlist, ordered by song_order. As of Cassandra 1.2, you do not need to include the ORDER BY column in the select expression.
所以基本上你只能通过要求 ASCending 或 DESCending 顺序来改变它.
So basically you can really only alter it by asking for ASCending or DESCending order.
您可能还想在 DataStax Ac*ademy 上查看使用 Apache Cassandra 在线课程的(免费)Java 开发一>.我相信会话 3 提供了一个关于 ORDER BY 子句的模块.
You also might want to check out the (free) Java development with Apache Cassandra online class at DataStax Ac*ademy. I believe session 3 offers a module on the ORDER BY clause.
编辑 2019
对于所有未来的 Google 员工，我在这篇博文大约一年后写了一篇关于这个主题的文章.它现在更旧了，但仍然与 Cassandra 的结果集排序相关:https://www.datastax.com/dev/blog/we-shall-have-order
For all future Googlers, I wrote an article on this topic about a year after this post. It's older now, but still relevant to result set ordering with Cassandra: https://www.datastax.com/dev/blog/we-shall-have-order
这篇关于在 cassandra 中使用 Order by 子句的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！