[jira] [Commented] (CASSANDRA-7017) allow per-partition LIMIT clause in cql

["Sylvain Lebresne (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-7017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14363407#comment-14363407 ] 

Sylvain Lebresne commented on CASSANDRA-7017:
---------------------------------------------

I'll note for the record that the attached patch actually doesn't work with paging, because if we page in the middle of a partition, we need to make sure we still fulfil the overall partition limitation. I'll further note that CASSANDRA-8099 actually solves that because it needed to for handling {{DISTINCT}} queries (or rather, that was the cleanest way I found). Or to put it another way, adding this on top of CASSANDRA-8099 would just amount to adding support for the syntax as the code handles it internally.


> allow per-partition LIMIT clause in cql
> ---------------------------------------
>
>                 Key: CASSANDRA-7017
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7017
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Halliday
>            Assignee: Dan Burkert
>              Labels: cql
>             Fix For: 3.0
>
>         Attachments: 0001-CASSANDRA-7017.patch
>
>
> somewhat related to static columns (#6561) and slicing (#4851), it is desirable to apply a LIMIT on a per-partition rather than per-query basis, such as to retrieve the top (most recent, etc) N clustered values for each partition key, e.g.
> -- for each league, keep a ranked list of users
> create table scores (league text, score int, player text, primary key(league, score, player) );
> -- get the top 3 teams in each league:
> select * from scores staticlimit 3;
> this currently requires issuing one query per partition key, which is tedious if all the key partition key values are known and impossible if they aren't.



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