I said its slow but I forget index. Now is as fast as a lightningbolt!!
Thanks again!
On Wed, Aug 19, 2009 at 12:23 PM, Mário Anselmo Scandelari Bussmann <
mario.bussm...@gmail.com> wrote:
> Bingo! This works very well (a little bit slow, since I have a 300000
> rows). Thank you all!!!
>
>
> On Wed, Aug 19, 2009 at 11:42 AM, John Machin <sjmac...@lexicon.net>wrote:
>
>> On 20/08/2009 12:10 AM, Mário Anselmo Scandelari Bussmann wrote:
>> > I have a table like this:
>> >
>> > petr4
>> > -----------
>> > rowid|data|preabe|premax|premin|preult|voltot
>> > 1|2007-01-02|50.0|50.45|49.76|50.45|256115409.0
>> > 2|2007-01-03|50.16|50.4|48.01|48.7|492591256.0
>> [snip]
>> > 9|2007-01-12|45.3|45.61|44.8|45.15|478912234.0
>> > 10|2007-01-15|45.61|45.85|44.89|44.89|317073087.0
>> >
>> > I need a select that returns data,preult,previous data and previous
>> preult:
>> >
>> > 2007-01-03|48.7|2007-01-02|50.45
>> > 2007-01-04|47.65|2007-01-03|48.7
>> [snip]
>> > 2007-01-12|45.15|2007-01-11|45.21
>> > 2007-01-15|44.89|2007-01-12|45.15
>> >
>> > How can I do that using only sql (no python, c or perl, no cursor)?
>>
>> No Python? How cruel :-)
>>
>> This works but you'd better have an index on 'data', and it looks like
>> at least O(N**2) OTTOMH:
>>
>> sqlite> create table x (data,preabe,premax,premin,preult,voltot);
>> sqlite> insert into x values
>> ('2007-01-02',50.0,50.45,49.76,50.45,256115409.0);
>> /* etc etc*/
>> sqlite> select a.data, a.preult, b.data, b.preult from x a, x b
>> ...> where b.data = (select max(c.data) from x c where c.data < a.data)
>> ...> order by a.data;
>> 2007-01-03|48.7|2007-01-02|50.45
>> 2007-01-04|47.65|2007-01-03|48.7
>> [snip]
>> 2007-01-12|45.15|2007-01-11|45.21
>> 2007-01-15|44.89|2007-01-12|45.15
>> sqlite>
>>
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>
>
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