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https://issues.apache.org/jira/browse/FLINK-7491?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16142277#comment-16142277
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Shuyi Chen commented on FLINK-7491:
-----------------------------------
Thanks for reviewing the PR. [~jark]
I think Multiset and Array are different, and they support different set of
operators (please see
http://farrago.sourceforge.net/design/CollectionTypes.html). Also, the calcite
definition of the COLLECT SqlAggFunction explicitly requires the return type to
be a Multiset (see below)
{code:java}
/**
* The COLLECT operator. Multiset aggregator function.
*/
public static final SqlAggFunction COLLECT =
new SqlAggFunction("COLLECT",
null,
SqlKind.COLLECT,
ReturnTypes.TO_MULTISET,
null,
OperandTypes.ANY,
SqlFunctionCategory.SYSTEM, false, false) {
};
{code}
I am worried that, if we use an Array to emulate a Multiset, going down the
path, we might have performance problem for large multiset, and potentially
calcite integration issues that are related to multiset. What do you think?
> Support COLLECT Aggregate function in Flink SQL
> -----------------------------------------------
>
> Key: FLINK-7491
> URL: https://issues.apache.org/jira/browse/FLINK-7491
> Project: Flink
> Issue Type: New Feature
> Components: Table API & SQL
> Reporter: Shuyi Chen
> Assignee: Shuyi Chen
>
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