Re: [h2] Are order of results always the same?

[Adam McMahon]

 

Thanks for your pointer on this.


What about this scenario:


I have a rather large table that I would like to process in the application 
in batches using a paging mechanism with OFFSET and LIMIT. I plan to do 
this in a simple loop which gets results N at a time, and each time 
increasing the OFFSET by N. I don't care the order in which these items are 
processed, but I need to make sure all are processed.


If subsequent SELECTS do not have the same order, does that effect the 
above scenario? In other words, if OFFSET/LIMIT trims the results sent back 
to the client, could the OFFSET/LIMIT be trimming at different places in 
the SELECT such that a loop with OFFSET/LIMIT never actually goes through 
the entire table, but instead sends back an arbitrary set.


For example, lets say I have a table with 50 names. I want to process these 
names 10 at a time, so I create a simple loop using OFFSET/LIMIT. Without 
adding in an ORDER BY, will it actually go through all 50 names. Or do I 
need to add an ORDERBY to ensure that the OFFSET knows what index to start 
at in the SELECT.


I hope this makes sense.


-Adam


On Wednesday, November 25, 2015 at 2:52:22 AM UTC-5, Noel Grandin wrote:
>
> You can't rely on that. If you need order, you need to enforce it with an 
> ORDER BY clause. 
>

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Re: [h2] Are order of results always the same?

[Thomas Mueller]

Hi,

You need to add "order by".

Regards,
Thomas


On Wed, Nov 25, 2015 at 5:05 PM, Adam McMahon  wrote:

> Thanks for your pointer on this.
>
>
> What about this scenario:
>
>
> I have a rather large table that I would like to process in the
> application in batches using a paging mechanism with OFFSET and LIMIT. I
> plan to do this in a simple loop which gets results N at a time, and each
> time increasing the OFFSET by N. I don't care the order in which these
> items are processed, but I need to make sure all are processed.
>
>
> If subsequent SELECTS do not have the same order, does that effect the
> above scenario? In other words, if OFFSET/LIMIT trims the results sent back
> to the client, could the OFFSET/LIMIT be trimming at different places in
> the SELECT such that a loop with OFFSET/LIMIT never actually goes through
> the entire table, but instead sends back an arbitrary set.
>
>
> For example, lets say I have a table with 50 names. I want to process
> these names 10 at a time, so I create a simple loop using OFFSET/LIMIT.
> Without adding in an ORDER BY, will it actually go through all 50 names. Or
> do I need to add an ORDERBY to ensure that the OFFSET knows what index to
> start at in the SELECT.
>
>
> I hope this makes sense.
>
>
> -Adam
>
>
> On Wednesday, November 25, 2015 at 2:52:22 AM UTC-5, Noel Grandin wrote:
>>
>> You can't rely on that. If you need order, you need to enforce it with an
>> ORDER BY clause.
>>
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> Visit this group at http://groups.google.com/group/h2-database.
> For more options, visit https://groups.google.com/d/optout.
>

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[h2] Are order of results always the same?

[Adam McMahon]

Hi,

It looks like the results of a querry are always given back in the same 
order.  Is this always true?  I know the order of a returned result is not 
the same as the insertion order.  But if a query is performed, and then 
repeated, will the result set be in the order (assuming the relevant tables 
have not changed?

Thanks,

-Adam 

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Re: [h2] Are order of results always the same?

[Noel Grandin]

You can't rely on that. If you need order, you need to enforce it with an ORDER 
BY clause.

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