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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7017) allow per-partition LIMIT clause in cql
Date Wed, 06 Apr 2016 13:57:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15228284#comment-15228284
] 

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

Looks good, thanks. I've started CI on the branch and will commit once it's done.

I did took the liberty to slightly modify the validation message from "SELECT DISTINCT queries
are not allowed with PER PARTITION LIMIT" to "PER PARTITION LIMIT is not allowed with SELECT
DISTINCT queries": same thing essentially but the first version made it more sound like the
limit was the "important part" (also changed the {{checkTrue(partitionLimit == null, ...)}}
to {{checkNull(partitionLimit, ...)}} since the method exists).

> 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: Alex Petrov
>              Labels: cql
>             Fix For: 3.x
>
>         Attachments: 0001-Allow-per-partition-limit-in-SELECT-queries.patch, 0001-Allow-per-partition-limit-in-SELECT-queriesV2.patch,
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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