Cassandra NOT EQUAL运算符 [英] Cassandra NOT EQUAL Operator

问题描述

对所有Cassandra专家的疑问.

Question to all Cassandra experts out there.

我有一个拥有大约一百万条记录的列族.

I have a column family with about a million records.

我想以某种方式查询这些记录，以便能够执行Not-Equal-To这种操作.

I would like to query these records in such a way that I should be able to perform a Not-Equal-To kind of operation.

我对此进行了谷歌搜索，看来我必须使用某种Map-Reduce.

I Googled on this and it seems I have to use some sort of Map-Reduce.

有人可以告诉我这方面有哪些选择.

Can somebody tell me what are the options available in this regard.

推荐答案

我可以建议一些方法.

I can suggest a few approaches.

1)如果您要测试的值数量有限，请考虑将其建模为boolean列(即:列isEqualToUnitedStates为true或false).

1) If you have a limited number of values that you would like to test for not-equality, consider modeling those as a boolean columns (i.e.: column isEqualToUnitedStates with true or false).

2)否则，请考虑通过组合客户端上两个单独的查询< X和> X的结果来模拟不受支持的查询!= X.

2) Otherwise, consider emulating the unsupported query != X by combining results of two separate queries, < X and > X on the client-side.

3)如果您的模式不能支持上述两种查询，则可能必须求助于编写自定义例程，该例程将进行客户端过滤并动态构造不相等的集合.如果您可以先将搜索空间缩小到可管理的比例，这样在没有不相等条件的情况下运行查询相对便宜，那么这将是可行的.

3) If your schema cannot support either type of query above, you may have to resort to writing custom routines that will do client-side filtering and construct the not-equal set dynamically. This will work if you can first narrow down your search space to manageable proportions, such that it's relatively cheap to run the query without the not-equal.

因此，假设您对除Widget之外的每种产品类型的特定客户的所有购买感兴趣.理想的查询可能类似于SELECT * FROM purchases WHERE customer = 'Bob' AND item != 'Widget';现在，您当然不能运行它，但是在这种情况下，您应该能够运行SELECT * FROM purchases WHERE customer = 'Bob'而不会浪费太多资源并在客户端应用程序中过滤item != 'Widget'.

So let's say you're interested in all purchases of a particular customer of every product type except Widget. An ideal query could look something like SELECT * FROM purchases WHERE customer = 'Bob' AND item != 'Widget'; Now of course, you cannot run this, but in this case you should be able to run SELECT * FROM purchases WHERE customer = 'Bob' without wasting too many resources and filter item != 'Widget' in the client application.

4)最后，如果在进行扫描之前无法以有意义的方式限制数据(不进行相等性检查的查询将返回太多行以致无法舒适地进行处理)，则您可能不得不求助于MapReduce.这意味着要运行一个分布式作业，该作业将扫描整个群集中表中的所有行.显然，此类作业的运行速度将比本地查询慢得多，并且设置起来非常复杂.如果您想采用这种方式，请查看 Cassandra Hadoop集成.

4) Finally, if there is no way to restrict the data in a meaningful way before doing the scan (querying without the equality check would returning too many rows to handle comfortably), you may have to resort to MapReduce. This means running a distributed job that would scan all rows in the table across the cluster. Such jobs will obviously run a lot slower than native queries, and are quite complex to set up. If you want to go this way, please look into Cassandra Hadoop integration.

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