Re: Query question

I do some tests with your first query and it seems to works.
Thanks a lot for your answer, i will post the final thought later
Thanks again
bye

Franco Bruno Borghesi wrote:

> If you have a row every 15 seconds, the answer is quite easy:
>
>SELECT
> A1.date
>FROM
> activity A1
> LEFT JOIN activity A2 ON (A2.date=A1.date-'15 secs'::interval)
>WHERE
> A1.state<>A2.state OR A2.state IS NULL
>ORDER BY 1
>
>
>
>
> Now if you don't have a row every 15 seconds, the answer is a bit more
> complex (at least I couldn't think of an easier solution):
>
>SELECT
> min(TMP2.new_date)
>FROM
> (
> SELECT
> DISTINCT
> TMP.new_date,
> max(TMP.old_date) AS max_old_date
> FROM
> (
> SELECT
> A1.id AS new_id, A1.date AS new_date, A1.state AS new_state,
> A2.id AS old_id, A2.date AS old_date, A2.state AS old_state
> FROM
> activity A1
> LEFT JOIN activity A2 ON (A2.date<A1.date)
> ORDER BY
> A1.date, A2.date DESC
> ) AS TMP
> WHERE
> TMP.old_state<>TMP.new_state OR TMP.old_state IS NULL
> GROUP BY
> TMP.new_date
> ) TMP2
>GROUP BY
> TMP2.max_old_date
>ORDER BY 1
>
>
>
> I've tested both queries on postgreSQL 8 with the data you provided,
> and they both work. Anyway try them with larger datasets before using
> them in real life ;-)
>
> Hope it helps.
>
>
> Stéphane RIFF wrote:
>
>> Hi ,
>>
>> I have table that represent a switch activity like this :
>>
>> | date | state |
>> | 2005-04-20 17:00:00 | 0 |
>> | 2005-04-20 17:00:15 | 0 |
>> | 2005-04-20 17:00:30 | 1 |
>> | 2005-04-20 17:00:45 | 1 |
>> | 2005-04-20 17:01:00 | 1 |
>> | 2005-04-20 17:01:15 | 0 |
>> | 2005-04-20 17:01:30 | 0 |
>> | 2005-04-20 17:01:45 | 0 |
>>
>> I want to get the date of each states change but i not a sql expert.
>> Can someone advices me
>>
>> Thanks
>>
>>
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