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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 Wysakowicz<dwysakowicz@xxxxxxxxxx>
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@xxxxxxx> 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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