[
https://issues.apache.org/jira/browse/CASSANDRA-8610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14304868#comment-14304868
]
Sylvain Lebresne commented on CASSANDRA-8610:
---------------------------------------------
I think we just forgot about it, no other non-obvious reason as far as I
remember.
> Allow IF EXISTS for UPDATE statements
> -------------------------------------
>
> Key: CASSANDRA-8610
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8610
> Project: Cassandra
> Issue Type: Improvement
> Components: API
> Environment: Cassandra 2.1.2
> Reporter: DOAN DuyHai
> Priority: Minor
> Attachments: 8610.patch
>
>
> While creating a hands-on exercice for Cassandra, I was facing a quite
> annoying limitation.
> Let's take this table:
> {code:sql}
> CREATE TABLE killrchat.chat_rooms(
> room_name text,
> creation_date timestamp,
> banner text,
> creator text,
> participants set<text>,
> PRIMARY KEY(room_name));
> {code}
> Upon a new participant joining the room, to be concurrency-proof (avoiding
> mutating the participants set if the room is deleted concurrently), I would
> like to issue this query:
> {code:sql}
> UPDATE chat_rooms SET participants = participants + {'johnny'} WHERE
> room_name = 'games' IF EXISTS;
> {code}
> Unfortunately the clause IF EXISTS is not allowed for UPDATE statements.
> Similarly I tried
> {code:sql}
> UPDATE chat_rooms SET participants = participants + {'johnny'} WHERE
> room_name = 'games' IF room_name='games';
> {code}
> It doesn't work either, it is not allowed to use one column of the primary
> key as condition column for LWT (why ? mystery).
> So far, the only work-around I found is:
> {code:sql}
> UPDATE chat_rooms SET participants = participants + {'johnny'} WHERE
> room_name = 'games' IF name='games';
> {code}
> I added an extra column called *name* which is just the duplicate of the
> partition key *room_name*. It does work but is not very elegant.
> I believe there are legit use cases for UPDATE ... IF EXISTS;
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
