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https://issues.apache.org/jira/browse/CASSANDRA-7494?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis resolved CASSANDRA-7494.
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Resolution: Not a Problem
I suggest exploring your use case on the user list. There may be cases where
CQL supports your goals only poorly, but the proposed solution is the wrong
solution for all of them.
> CQL support to return first column of each row
> ----------------------------------------------
>
> Key: CASSANDRA-7494
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7494
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Environment: fedora 64bit
> Reporter: Samphel Norden
>
> This jira is a request to support a query like
> select first 5 columns of each row where <whereclause>
> Currently in CQL, if we put a limit clause it applies over all rows. Not a
> per partition key limit.
> More details below
> IF we create a table as follows
> CREATE TABLE xy (
> a int,
> b int,
> c int,
> d int,
> value int,
> PRIMARY KEY ((a, b), c, d)
> ) WITH CLUSTERING ORDER BY (c DESC, d ASC)
> with data =
> a | b | c | d | value
> --------------
> 1 | 2 | 2007 | 307 | 950
> 1 | 2 | 2006 | 305 | 900
> 1 | 1 | 1006 | 205 | 800
> 1 | 1 | 1005 | 105 | 700
> The rows are sorted by c descending where assuming c is a timestamp, the idea
> is to store the latest timestamp first. Hence if we pull a single column from
> each row given a set of rows, we want that to be the latest 'c' for each row.
> In other words:
> select first 1 value from xy where a=1 and b in (1,2)
> should return a single "value" for each rowkey
> a | b | c | d | value
> --------------
> 1 | 1 | 1006 | 205 | 800
> 1 | 2 | 2007 | 307 | 950
> I realize that if we do individual queries such as
> select a,b,c,value from xy where a=1 and b =1 limit 1;
> a | b | c | value
> -------+----
> 1 | 1 | 1006 | 800
> (1 rows)
> cqlsh:> select a,b,c,e from xy where a=1 and b =2 limit 1;
> a | b | c | value
> -------+----
> 1 | 2 | 2007 | 950
> We get the desired result.However this is highly inefficient since we would
> need to fire a separate query per row. If we can have a construct change to
> allow getting a single column for a given row that would be very helpful
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