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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-4851) CQL3: improve support for paginating over composites
Date Tue, 23 Oct 2012 16:31:14 GMT
Sylvain Lebresne created CASSANDRA-4851:
-------------------------------------------

             Summary: CQL3: improve support for paginating over composites
                 Key: CASSANDRA-4851
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4851
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Sylvain Lebresne
            Priority: Minor


Consider the following table:
{noformat}
CREATE TABLE test (
    k int,
    c1 int,
    c2 int,
    PRIMARY KEY (k, c1, c2)
)
{noformat}
with the following data:
{noformat}
k | c1 | c2
------------
0 | 0  | 0
0 | 0  | 1
0 | 1  | 0
0 | 1  | 1
{noformat}
Currently, CQL3 allows to slice over either c1 or c2:
{noformat}
SELECT * FROM test WHERE k = 0 AND c1 > 0 AND c1 < 2
SELECT * FROM test WHERE k = 0 AND c1 = 1 AND c2 > 0 AND c2 < 2
{noformat}
but you cannot express a query that return the 3 last records. Indeed, for that you would
need to do a query like say:
{noformat}
SELECT * FROM test WHERE k = 0 AND ((c1 = 0 AND c2 > 0) OR c2 > 0)
{noformat}
but we don't support that.

This can make it hard to paginate over say all records for {{k = 0}} (I'm saying "can" because
if the value for c2 cannot be very large, an easy workaround could be to paginate by entire
value of c1, which you can do).

For the case where you only paginate to avoid OOMing on a query, CASSANDRA-4415 will that
and is probably the best solution. However, there may be case where the pagination is say
user (as in, the user of your application) triggered.

I note that one solution would be to add the OR support at least in case like the one above.
That's definitively doable but on the other side, we won't be able to support full-blown OR,
so it may not be very natural that we support seemingly random combination of OR and not others.

Another solution would be to allow the following syntax:
{noformat}
SELECT * FROM test WHERE k = 0 AND (c1, c2) > (0, 0)
{noformat}
which would literally mean that you want records where the values of c1 and c2 taken as a
tuple is lexicographically greater than the tuple (0, 0). This is less SQL-like (though maybe
some SQL store have that, it's a fairly thing to have imo?), but would be much simpler to
implement and probably to use too.


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