On Mon, Jul 11, 2022 at 7:25 AM ashwin k <ashwin...@gmail.com> wrote:
> It would be appreciated If you could correct me if Im incorrect.When
> offset
> is zero getting columns is not required;
>
Correct, because offset of 0 is the same as no offset at all.
when offset is greater than zero why columns are required ?
>
Emulating offset on old versions of Oracle requires a query where the
underlying columns must be specified. Oracle didn't start natively
supporting offsets until Oracle 12. So if you want to avoid this query,
update to Oracle 12 (or use a different database).
Thanks,
Jeremy
>
> On Mon, 11 Jul, 2022, 7:44 pm Jeremy Evans, <jeremyeva...@gmail.com>
> wrote:
>
>> On Mon, Jul 11, 2022 at 1:54 AM ashwin k <ashwin...@gmail.com> wrote:
>>
>>> The extra query is getting triggered only when offset is greater than
>>> zero.
>>>
>>> I didn't notice this query when offset is zero.
>>>
>>
>> When offset is zero, the query to get the columns is not necessary, so
>> Sequel doesn't issue it.
>>
>> Thanks,
>> Jeremy
>>
>>
>>> On Sun, 10 Jul, 2022, 10:39 pm Jeremy Evans, <jeremyeva...@gmail.com>
>>> wrote:
>>>
>>>> On Sun, Jul 10, 2022 at 1:51 AM ashwin k <ashwin...@gmail.com> wrote:
>>>>
>>>>> Not sure if first query can be ignored?
>>>>>
>>>>
>>>> Not sure what you mean by "can be ignored". It's necessary to get the
>>>> columns, and you need to know the columns to create the second query.
>>>>
>>>> Thanks,
>>>> Jeremy
>>>>
>>>>
>>>>>
>>>>> On Sat, 9 Jul, 2022, 11:52 am Jeremy Evans, <jeremyeva...@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> On Fri, Jul 8, 2022 at 9:41 PM ashwin k <ashwin...@gmail.com> wrote:
>>>>>>
>>>>>>> Limit fires an extra query when the offset is more than 1. I created
>>>>>>> a temp table and executed the query
>>>>>>> DB[:temp].limit(3,3).all
>>>>>>>
>>>>>>> *First it executed this query*
>>>>>>> START SELECT * FROM (SELECT * FROM "TEMP") "T1" WHERE (ROWNUM <= 1)
>>>>>>> - END ( 0.0060s) SELECT * FROM (SELECT * FROM "TEMP") "T1" WHERE
>>>>>>> (ROWNUM <= 1)
>>>>>>>
>>>>>>> *and then this*
>>>>>>>
>>>>>>> - START SELECT "ID", "NAME" FROM (SELECT "T1".*, ROWNUM
>>>>>>> "X_SEQUEL_ROW_NUMBER_X" FROM (SELECT * FROM "TEMP") "T1") "T1" WHERE
>>>>>>> (("X_SEQUEL_ROW_NUMBER_X" > 3) AND ("X_SEQUEL_ROW_NUMBER_X" <= (3 + 3)))
>>>>>>>
>>>>>>> - END ( 0.0033s) SELECT "ID", "NAME" FROM (SELECT "T1".*, ROWNUM
>>>>>>> "X_SEQUEL_ROW_NUMBER_X" FROM (SELECT * FROM "TEMP") "T1") "T1" WHERE
>>>>>>> (("X_SEQUEL_ROW_NUMBER_X" > 3) AND ("X_SEQUEL_ROW_NUMBER_X" <= (3 +
>>>>>>> 3))) =>
>>>>>>> [{:id=>0.4e1, :name=>"d"}, {:id=>0.5e1, :name=>"e"}]
>>>>>>>
>>>>>>
>>>>>> Not sure what database you are using, but I'm guessing an old version
>>>>>> of Oracle? In order to run the query with a limit and offset on an old
>>>>>> version of Oracle, the limit and offset need to be emulated using ROWNUM,
>>>>>> and that requires getting the columns. The first query is run to get the
>>>>>> columns, and the second query to get the data (you can see the second
>>>>>> query
>>>>>> uses the columns returned by the first query).
>>>>>>
>>>>>> Thanks,
>>>>>> Jeremy
>>>>>>
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