Re: problem with a query

Użytkownik Carlos Sousa napisał:
> hi to all
>
> i need to do a query to a small postgres database
> my best efort to the pretended query is in the attached file 'query.txt'
> but i need that some rows don't be selected of thouse that the query
> returns.
>
> i send in another attached file 'result.txt' with the query result.
> looking at content of the file you will see some notes at the end of the
> table (#..)
>
> the database as the data to enable the constrution of a school class
> schedule.
>
> In the 'result.txt' all the rows with max=0 were the fisrt to be
> inserted do the database. each row represent as example math pratical
> starting at 8:30 for 1:30 at room 3.15 in the bilding CP
>
> the rows with max!=0 (1,2,3,...) mean that content of an insert with
> max=0 was changed [ex diferent time (fiel to_char) or room (field sala)
> or bilding (field edificio)of the school class]. row with max=1 is a
> substitution to a row with max=0, row with max=2 substitutes row with
> max=1 and ...
>
> my objective is to obtain all the rows that were not substituted and the
> ones that represent the last alteration to the shedule
>
> i hope the problem was understod
I'm not sure, but you want to get data for each room (field "sala") with
the biggest field "indice"?
you can do this with query:
select distinct on (indice)
...
from
...
order by sala,indice desc;

Result of this query is - one row per one "sala". If there are more then
1 records in database with the same "sala", you get record with biggest
"indice". You don't need to use max(indice) and group by...

Tomasz Myrta