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https://issues.apache.org/jira/browse/CALCITE-1237?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15288687#comment-15288687
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Fabian Hueske commented on CALCITE-1237:
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Hi [~julianhyde], thanks for the proposal! I like it.
Answering your questions first:
Q1: In my opinion "at most" is more intuitive than "less than".
Q2: I'm in favor of allowing order-dependent aggregates
Q3: I think supporting {{session}} in the {{GROUP BY}} clause is a good
starting point.
I have a few questions / suggestions as well:
- is it possible to move the additional grouping columns out of the {{session}}
function to the {{GROUP BY}} clause? This would be more similar to the
definition of {{TUMBLE}} and {{HOP}} in
http://calcite.apache.org/docs/stream.html?
- Can we add functions similar to {{TUMBLE_START}} and {{TUMBLE_END}}? It would
be consistent with the other window functions and a shortcut compared to
accessing the corresponding values with {{first_value}} and {{last_value}}
(given that we allow order-dependent aggregates).
- You said "Unlike the tumble function, each row belongs to precisely one
window.". Tumbling windows are non-overlapping, so {{tumble}} should be
{{hop}}, right?
> Session windows for streaming SQL
> ---------------------------------
>
> Key: CALCITE-1237
> URL: https://issues.apache.org/jira/browse/CALCITE-1237
> Project: Calcite
> Issue Type: Bug
> Components: stream
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> A session window is a collection of rows whose key values, when sorted, have
> a gap of at most N.
> Q1. Should "at most" be "less than"?
> The key type can be any type that has a minus operator, that is, numeric and
> date-time.
> I propose the following syntax: {{session(key [, ...]*, interval)}}. For
> example:
> {code}
> select stream session(rowtime, productId, interval '5' second),
> productId, count(*) as c
> from Orders
> group by session(rowtime, productId, interval '5' second),
> productId
> {code}
> to find bursts of orders for the same product where consecutive orders are no
> more than 5 seconds apart.
> The first key column {{rowtime}} defines the session and must be of
> numeric/date-time type, and must have monotonicity or similar in order for
> the query to make progress; the other key columns (in this case
> {{productId}}) can be of any type; the last column is the interval, and must
> be constant.
> The {{session}} function returns the key value at the start of the window.
> Unlike the {{tumble}} function, each row belongs to precisely one window. But
> {{session}} is not a true function, because its value depends on the records
> flowing in the stream.
> Q2. If {{session}} is used, should we allow order-dependent aggregate
> functions such as {{first_value}}?
> Q3. Should we allow {{session}} as a windowed aggregate function?
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