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From "Aleksey Plekhanov (Jira)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-14443) Calcite integration. SqlFirstLastValueAggFunction support
Date Wed, 09 Jun 2021 08:57:00 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-14443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17359877#comment-17359877
] 

Aleksey Plekhanov commented on IGNITE-14443:
--------------------------------------------

{{FIRST_VALUE}}/\{{LAST_VALUE}} aggregates are windows functions and can't be used without
windows support. I've tried to make it work without windows (in attached PR) but looks like
it makes little sense since it's hard to influence the underlying input ordering and hard
to predict what entries {{FIRST_VALUE}}/\{{LAST_VALUE}} will return (especially in a distributed
environment) without knowledge of the internal implementation. For example, in query:
{code:java}
select first_value(name) from (select * from person order by id)
{code}
Clause {{ORDER BY id}} is eliminated by the optimizer and there are no guarantees that first
by id name will be returned. To ensure ordering {{OVER (ORDER BY id)}} clause can be used
when windows function will be supported. 

I think without windows support {{ANY_VALUE}} aggregate can be used in most cases.

> Calcite integration. SqlFirstLastValueAggFunction support
> ---------------------------------------------------------
>
>                 Key: IGNITE-14443
>                 URL: https://issues.apache.org/jira/browse/IGNITE-14443
>             Project: Ignite
>          Issue Type: New Feature
>          Components: sql
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Pavel Vinokurov
>            Assignee: Aleksey Plekhanov
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> We need to support aggregation functions, especially SqlFirstLastValueAggFunction that
allows simplify and optimize the wide range of sql queries.



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