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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