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From "bupt_ljy"<bupt_...@163.com>
Subject Re: Problems about subsets clause order for MATCH_RECOGNIZE
Date Mon, 17 Dec 2018 09:05:52 GMT
Hi,
  It makes sense to me.
  Thanks for the introductions.


Best,
Jiayi Liao


Original Message
Sender:Dawid Wysakowiczdwysakowicz@apache.org
Recipient:bupt_ljybupt_ljy@163.com; devdev@calcite.apache.org; Julian Hydejhyde@apache.org
Date:Monday, Dec 17, 2018 16:52
Subject:Re: Problems about subsets clause order for MATCH_RECOGNIZE


Hi Jiayi,
not sure what you mean by elements' order in SUBSET, so I'd try to rephrase it. What I mean
is that the order of pattern variables in SUBSET clause does not matter. User can put them
in whatever order he/she likes. LAST/FIRST etc. will account for the order in PATTERN clause.
So in general (SUBSET X = (A,B)) = (SUBSET X = (B,A)). This is my understanding from[1]. Also
it would be nice to actually verify this behavior with ORACLE.

Can not tell anything about concrete implementation decisions though. Don't know why sortedSet
was used there.
Best,
Dawid



[1] https://standards.iso.org/ittf/PubliclyAvailableStandards/c065143_ISO_IEC_TR_19075-5_2016.zip

On 17/12/2018 04:52, bupt_ljy wrote:

Hi Dawid,
 The elements’s order in SUBSET clause is consistent with the order in PATTERN, is this
what you mean?
 
 Let me take an example:  SUBSET X=(A,B)


 I’m not very sure about the implementations of Oracle, but I’m curious that why we use
sortedSet to store the elements(A,B) of SUBSET if we don’t need the “sorted”.


Best,
Jiayi Liao


Original Message
Sender:Dawid Wysakowiczdwysakowicz@apache.org
Recipient:devdev@calcite.apache.org; Julian Hydejhyde@apache.org; bupt_ljybupt_ljy@163.com
Date:Sunday, Dec 16, 2018 20:08
Subject:Re: Problems about subsets clause order for MATCH_RECOGNIZE


Hi Jiayi, I don't think it should any difference what is the order in the SUBSET clause. The
PATTERN clause specifies the definitive order of pattern variables. SUBSET clause just groups
them as a single entity you can reference. Therefore LAST/FIRST/PREV/NEXT/AFTER MATCH etc.
will take into account only order in the PATTERN clause. Best, Dawid On 16/12/2018 08:07,
Julian Hyde wrote:  I don’t understand MATCH_RECOGNIZE well enough to give an opinion. Is
there a query that gives different results on Oracle if you change the order of items in SUBSET?
  It seems that the parser preserves the order of items in the subset, but the SqlToRelConverter
does not, hence the line "subsets=[[[DOWN, STRT]]” in SqlToRelConverterTest.xml. I would
be concerned if the parser re-ordered things, but I am not too concerned about SqlToRelConverter
unless the semantics are wrong.   On Dec 14, 2018, at 12:37 AM, bupt_ljy bupt_ljy@163.com
wrote:   Hi all,  It’s my first time to send emails to Calcite developers. It’s a really
good project and many projects benefit from it.  Now I’ve encountered a problem about the
subsets for MATCH_RECOGNIZE in thetestMatchRecognizeSubset1() testing. From the results, I
can tell that"subset stdn = (strt, down)"will be explained to "SUBSET \"STDN\" = (\"DOWN\",
\"STRT\”)”, which confuses me. IMO, It’ll affect the result of functions like“FIRST”
and“LAST”, which may not be what I want, although it works fine with“AVG” function.
 I’m not sure if this is a bug, or anyone can tell me how we arrive here?      Best,  Jiayi
Liao
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