CQL中每个记录的限制列 [英] Limiting columns per record in CQL

问题描述

我有一个问题，从现在开始一直困扰着我.为了简化起见，我将其缩小了.

I've a problem which has been bothering me from quite while now. I'm scaling it down for simplification.

我在Cassandra中有一个列族定义为:

I've a column family in Cassandra defined as:

  CREATE TABLE "Test" (
  key text,                         
  column1 text,                    
  value text,                        
  PRIMARY KEY (key, column1)       
)

如果我在CQL中以以下方式运行查询:

If I run a query in CQL as:

select * from "Test" where key in ('12345','34567');

它给了我类似的东西

  key  | column1 | value
-----------------------+---
 12345 |     764 |    764
 12345 |     836 |    836
 12345 |  123723 | 123723
 12345 |  155863 | 155863

  key  | column1 | value
-----------------------+---
 34567 |  159144 | 159144
 34567 |  159869 | 159869
 34567 |  160705 | 160705

现在我的问题是如何将我的结果限制为每条记录最多2行.我尝试使用以下内容，但没有用.

Now my question is how can I limit my results to 2 rows max per record. I tried to use the following but didn't work.

select FIRST 10 'a'..'z' from "Test" where key in ('12345','34567'); 

-在最新的CQL版本中不可用.

- Not available in latest CQL version.

select * from "Test" where key in ('12345','34567') limit 2;

-仅限制总行数，而不是每条记录

-Only limits total number of rows, not per record

推荐答案

CQL3中没有这种类型的限制.您必须为每个分区运行一个单独的查询.

There is no way to have this type of limit in CQL3. You have to run a separate query for each partition.

如果查询延迟对您而言不是问题，那么您始终可以在Cassandra数据库之上安装SparkSQL/Hive，以进行复杂的分析查询，例如原始问题中的查询.您甚至可以缓存这些查询的结果.

If query latency is not an issue for you, you always can install SparkSQL/Hive on top of your Cassandra database for complex analytical queries like the one in your original question. You even can cache the result of these queries.

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