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Date: Tue, 5 Mar 2013 18:24:13 +0000 (UTC)
From: "Ahmet AKYOL (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12635318.1362480390343.385128.1362507853473@arcas>
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Subject: [jira] [Commented] (CASSANDRA-5313) provide a cardinality function
 for collection types ( CQL3 )
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    [ https://issues.apache.org/jira/browse/CASSANDRA-5313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13593710#comment-13593710 ] 

Ahmet AKYOL commented on CASSANDRA-5313:
----------------------------------------

{quote} but there is always the worry that people will expect it to be smarter than that when it isn't {quote} 
that's why I told my wish "maybe mixing counter columns and other data types in a table could be better ". I also said "from schema design point of view" because I didn't figure how to design my use case yet.Perhaps, it's time for you (guys) to write a "Cassandra in action" book since cql 3 is a bit [mystery even for experts|http://www.datastax.com/dev/blog/cql3-for-cassandra-experts]. I assure you, I'll be the first one to buy it in [MEAP|http://www.manning.com/about/meap.html] :)

Anyway, maybe this feature still can be useful for lazy loading. what I mean is, we can only store keys of another table in a set for uniqueness and still query the count (cardinality) in cql without any trick. 
                
> provide a cardinality function for collection types ( CQL3 )
> ------------------------------------------------------------
>
>                 Key: CASSANDRA-5313
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5313
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Ahmet AKYOL
>              Labels: cql3, ponies
>
> Currently , cql3 doesn't provide a cardinality function for collection types. It'll be great to have one:
> {code}
> select content, cardinality(like_set),cardinality(dislike_set) from comments where id=?;
> {code}
> or size as keyword
> {code}
> select content, size(like_set),size(dislike_set) from comments where id=?;
> {code}
> Something similar in SQL is [cardinality of nested tables|http://www.techonthenet.com/oracle/functions/cardinality.php] .

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