Użytkownik Carlos Sousa napisał:
hi to allI'm not sure, but you want to get data for each room (field "sala") with the biggest field "indice"?
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
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
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