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From Steven Jacobs <sjaco...@ucr.edu>
Subject Re: Nonpure functions in the context of SQL++
Date Tue, 18 Apr 2017 20:33:18 GMT
I realized that putting it first in the list of from might make sense, but
it's unclear to me how to make it be treated as a value rather than a
sequence in this case, e.g. I tried the following:
insert into channels.EmergencyChannelResults as a (
select result, channelExecutionTime, sub.subscriptionId as
subscriptionId,current_datetime() as deliveryTime
from current_datetime()  channelExecutionTime, Metadata.Broker b,
channels.EmergencyChannelSubscriptions sub,
channels.RecentEmergenciesNearUser(sub.param0) result
where b.BrokerName= sub.BrokerName and b.DataverseName= sub.DataverseName
) returning a;

But this gives me an error for trying to treat the value as a collection,
i.e.

unnest $$0 <- function-call: asterix:scan-collection, Args:[function-call:
asterix:current-datetime, Args:[]] -- |UNPARTITIONED|

Steven

On Tue, Apr 18, 2017 at 1:23 PM, Steven Jacobs <sjaco002@ucr.edu> wrote:

> Hi all,
> I'm currently trying to switch the BAD project to SQL++, and having an
> issue with non pure function calls. In AQL, a let non-pure assignment (e.g.
> current-time) before a for statement means that the assignment should
> return a single value for all uses under the for. I optimized the rewrite
> rules to handle this case (The assignment will start out above an
> empty-tuple-source, meaning that it's called once in the initial plan).
>
> In SQL++, the last statement isn't true. If you do a let assignment before
> a select, the assignment starts out baked into the result object
> constructor, which means that it starts out inherently being called on a
> per-result-object basis.
>
> It's unclear to me how this stuff should be handled in SQL++ syntax. Is
> there an inherent way to tell the parser that a "let" should be done only
> once?
>
> Steven
>

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