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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5715) CAS on 'primary key only' table
Date Fri, 05 Jul 2013 08:37:52 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13700533#comment-13700533
] 

Sylvain Lebresne commented on CASSANDRA-5715:
---------------------------------------------

I agree, that's the other possible choice. However, since CQL does not do any difference between
INSERT and UPDATE without condition and they are both UPSERT, I think I have a net preference
for assuming that we differ from SQL here and supporting all the variations since they do
make sense for CQL. That is, I'd rather not focus on the fact that a SQL reading sounds slightly
off. A more practical reason for supporting all variations is tooling: I can imagine it being
slightly simpler for a high level API to be able only generate UPDATE under the hood (the
same way some thrift client probably only ever use batch_mutate(), never insert()) rather
than having special casing just because of the "IF".
                
> CAS on 'primary key only' table
> -------------------------------
>
>                 Key: CASSANDRA-5715
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5715
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>             Fix For: 2.0
>
>         Attachments: 0001-Conditions-on-INSERT.txt, 0002-Support-updating-the-PK-only.txt
>
>
> Given a table with only a primary key, like
> {noformat}
> CREATE TABLE test (k int PRIMARY KEY)
> {noformat}
> there is currently no way to CAS a row in that table into existing because:
> # INSERT doesn't currently support IF
> # UPDATE has no way to update such table
> So we should probably allow IF conditions on INSERT statements.
> In addition (or alternatively), we could work on allowing UPDATE to update such table.
One motivation for that could be to make UPDATE always be more general to INSERT. That is
currently, there is a bunch of operation that INSERT cannot do (counter increments, collection
appends), but that "primary key table" case is, afaik, the only case where you *need* to use
INSERT. However, because CQL forces segregation of PK value to the WHERE clause and not to
the SET one, the only syntax that I can see work would be:
> {noformat}
> UPDATE WHERE k=0;
> {noformat}
> which maybe is too ugly to allow?
>  

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