[
https://issues.apache.org/jira/browse/CASSANDRA-18073?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Andres de la Peña updated CASSANDRA-18073:
------------------------------------------
Description:
The CQL native aggregate function {{avg}} returns zero when it's applied to an
empty set of values:
{code:java}
> CREATE TABLE t (k int PRIMARY KEY, v int);
> SELECT avg(v) FROM t;
system.avg(v)
---------------
0
{code}
The new {{collection_avg}} that has just been added by CASSANDRA-18060 is based
on the {{avg}} implementation, so both are consistent. Thus, it will also
return zero for an empty collection:
{code:java}
> CREATE TABLE t (k int PRIMARY KEY, v frozen<set<int>>);
> INSERT INTO t (k,v) VALUES(1, {});
> SELECT collection_avg(v) FROM t;
system.collection_avg(v)
--------------------------
0
{code}
I think these functions should probably better return {{NaN}} instead of zero.
However, returning zero is not terribly incorrect, and returning {{NaN}} might
be problematic for backward compatibility.
Also, to further complicate things, {{BigInteger}} and {{BigDecimal}} don't
have a {{NaN}} value, so {{avg}} for {{varint}} and {{decimal}} should have a
different behaviour, such as:
* Keep returning zero
* Return {{null}}
* Throw an exception
was:
The CQL native aggregate function {{avg}} returns zero when it's applied to an
empty set of values:
{code:java}
> CREATE TABLE t (k int PRIMARY KEY, v int);
> SELECT avg(v) FROM t;
system.avg(v)
---------------
0
{code}
The {{collection_avg}} that is about to be added by CASSANDRA-18060 is based on
the {{avg}} implementation, so both are consistent. Thus, it will also return
zero for an empty collection:
{code:java}
> CREATE TABLE t (k int PRIMARY KEY, v frozen<set<int>>);
> INSERT INTO t (k,v) VALUES(1, {});
> SELECT collection_avg(v) FROM t;
system.collection_avg(v)
--------------------------
0
{code}
I think these functions should probably better return {{NaN}} instead of zero.
However, returning zero is not terribly incorrect, and returning {{NaN}} might
be problematic for backward compatibility.
Also, to further complicate things, {{BigInteger}} and {{BigDecimal}} don't
have a {{NaN}} value, so {{avg}} for {{varint}} and {{decimal}} should have a
different behaviour, such as:
* Keep returning zero
* Return {{null}}
* Throw an exception
> AVG CQL function of an empty set of values returns zero
> -------------------------------------------------------
>
> Key: CASSANDRA-18073
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18073
> Project: Cassandra
> Issue Type: Bug
> Components: CQL/Semantics
> Reporter: Andres de la Peña
> Priority: Normal
>
> The CQL native aggregate function {{avg}} returns zero when it's applied to
> an empty set of values:
> {code:java}
> > CREATE TABLE t (k int PRIMARY KEY, v int);
> > SELECT avg(v) FROM t;
> system.avg(v)
> ---------------
> 0
> {code}
> The new {{collection_avg}} that has just been added by CASSANDRA-18060 is
> based on the {{avg}} implementation, so both are consistent. Thus, it will
> also return zero for an empty collection:
> {code:java}
> > CREATE TABLE t (k int PRIMARY KEY, v frozen<set<int>>);
> > INSERT INTO t (k,v) VALUES(1, {});
> > SELECT collection_avg(v) FROM t;
> system.collection_avg(v)
> --------------------------
> 0
> {code}
> I think these functions should probably better return {{NaN}} instead of zero.
> However, returning zero is not terribly incorrect, and returning {{NaN}}
> might be problematic for backward compatibility.
> Also, to further complicate things, {{BigInteger}} and {{BigDecimal}} don't
> have a {{NaN}} value, so {{avg}} for {{varint}} and {{decimal}} should have a
> different behaviour, such as:
> * Keep returning zero
> * Return {{null}}
> * Throw an exception
>
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
