Обсуждение: Aggregates and Joins
Hello,
I've kind of run into a wall, just now, and I don't know if I can climb it
with Postgres. In order to fully explain my problem, I've got to actually
go into detail about my database setup... so, if you're willing to
listen/read for a minute, I appreciate it. Just so you know, my problem -
as I see it - is related to the limitation of aggregate function use.
In my database, I have two tables. In one of the tables, I have a primary
key 'trans_id'. In the other table, I store vital information associated
with 'trans_id'. More specifically:
table first_table (
trans_id int, -- my primary key
otherfields blah
blah blah
);
table second_table (
this_id int,
price money,
...
..
trans_id int, -- my primary key association
);
In second_table, there may be any number (greater than zero) of records
associated with a single record in first_table (ie. if I have a record in
frist_table with a 'trans_id' = 33, I may have 1 or 100 records in
second_table with a 'trans_id' = 33).
What I need to do is to obtain the sum of the field 'price' from
second_table for every distinct 'trans_id' (all of which can be found in
first_table). Right now, I do not know of any way to do this, other than
by using my scripting language to first get all of the 'trans_id' values
from first_table - "select trans_id from first_table" - and then (for
each and every one of the records returned) initiating a separate query -
"select sum(price) from second_table where trans_id = onetransid" - that
would use the aggregate function sum() on the price field in second_table.
This isn't a problem if I'm only trying to get the sum(price) for a
hundred or so distinct 'trans_id' values. However, I will (more often
than not) be trying to do this for thousands of distinct 'trans_id'
values. Is there a quicker way to do this? Is it possible to use the
aggregate functions and have more than one row returned?
Here's some pseudo-code to look at, if you'd like:
// set up the query
$query = "select trans_id from first_table";
// execute the query and obtain a pointer to the results
$result = dbExec($postgresConnection, $query);
// find out how many records were returned
$numrecords = pg_NumRows($result);
// obtain the 'trans_id' values, one by one, and sum() the price
for($i = 0; $i < $numrecords; $i++) {
$trans_id = pg_Result($result, $i, 0); // record $i, index 0
$subquery = "select sum(price) from second_table " .
"where trans_id = $trans_id";
$subresult = dbExec($postgresConnection, $subquery);
// only one record - to my knowledge - can be returned
$pricesum[$trans_id] = pg_Result($result, 0, 0);
}
Any help you can give will be graciously accepted.....
Thanks,
Bob
Bob Dusek wrote: ... >table second_table ( > > this_id int, > price money, > ... > .. > trans_id int, -- my primary key association > >); ... >What I need to do is to obtain the sum of the field 'price' from >second_table for every distinct 'trans_id' (all of which can be found in >first_table). ... Is there a quicker way to do this? Is it possible to >use the aggregate functions and have more than one row returned? select sum(price) from second_table group by trans_id; -- Oliver Elphick Oliver.Elphick@lfix.co.uk Isle of Wight http://www.lfix.co.uk/oliver PGP key from public servers; key ID 32B8FAA1 ======================================== "Jesus saith unto him, I am the way, the truth, and the life; no man cometh unto the Father, but by me." John 14:6
Hey!!! Thanks a lot. That is just what I needed. here's the query I used: select sum(price), trans_id from second_table group by trans_id; I had to include the "trans_id" in the target list to use it for grouping. I've never been able to mix single fields and aggregates before (of course, I've never used the "group" syntax before either). Thanks a lot. Bob On Tue, 24 Nov 1998, Oliver Elphick wrote: > Date: Tue, 24 Nov 1998 23:30:19 +0000 > From: Oliver Elphick <olly@lfix.co.uk> > To: Bob Dusek <bobd@palaver.net> > Cc: PostgreSQL General <pgsql-general@postgreSQL.org> > Subject: Re: [GENERAL] Aggregates and Joins > > Bob Dusek wrote: > ... > >table second_table ( > > > > this_id int, > > price money, > > ... > > .. > > trans_id int, -- my primary key association > > > >); > ... > >What I need to do is to obtain the sum of the field 'price' from > >second_table for every distinct 'trans_id' (all of which can be found in > >first_table). ... Is there a quicker way to do this? Is it possible to > >use the aggregate functions and have more than one row returned? > > select sum(price) from second_table group by trans_id; > > -- > Oliver Elphick Oliver.Elphick@lfix.co.uk > Isle of Wight http://www.lfix.co.uk/oliver > PGP key from public servers; key ID 32B8FAA1 > ======================================== > "Jesus saith unto him, I am the way, the truth, and the > life; no man cometh unto the Father, but by me." > John 14:6 > > >
Hello
If I have well understood what you want, you can do it by using a "group
by" clause. In the case you proposed, it should be used like:
select ref, sum(price)
from second_table
group by trans_id ;
I've tried this and it works for my database. Hope it helps
Bob Dusek wrote:
>
> Hello,
>
> I've kind of run into a wall, just now, and I don't know if I can climb it
> with Postgres. In order to fully explain my problem, I've got to actually
> go into detail about my database setup... so, if you're willing to
> listen/read for a minute, I appreciate it. Just so you know, my problem -
> as I see it - is related to the limitation of aggregate function use.
>
> In my database, I have two tables. In one of the tables, I have a primary
> key 'trans_id'. In the other table, I store vital information associated
> with 'trans_id'. More specifically:
>
> table first_table (
>
> trans_id int, -- my primary key
> otherfields blah
> blah blah
>
> );
>
> table second_table (
>
> this_id int,
> price money,
> ...
> ..
> trans_id int, -- my primary key association
>
> );
>
> In second_table, there may be any number (greater than zero) of records
> associated with a single record in first_table (ie. if I have a record in
> frist_table with a 'trans_id' = 33, I may have 1 or 100 records in
> second_table with a 'trans_id' = 33).
>
> What I need to do is to obtain the sum of the field 'price' from
> second_table for every distinct 'trans_id' (all of which can be found in
> first_table). Right now, I do not know of any way to do this, other than
> by using my scripting language to first get all of the 'trans_id' values
> from first_table - "select trans_id from first_table" - and then (for
> each and every one of the records returned) initiating a separate query -
> "select sum(price) from second_table where trans_id = onetransid" - that
> would use the aggregate function sum() on the price field in second_table.
> This isn't a problem if I'm only trying to get the sum(price) for a
> hundred or so distinct 'trans_id' values. However, I will (more often
> than not) be trying to do this for thousands of distinct 'trans_id'
> values. Is there a quicker way to do this? Is it possible to use the
> aggregate functions and have more than one row returned?
>
> Here's some pseudo-code to look at, if you'd like:
>
> // set up the query
> $query = "select trans_id from first_table";
> // execute the query and obtain a pointer to the results
> $result = dbExec($postgresConnection, $query);
>
> // find out how many records were returned
> $numrecords = pg_NumRows($result);
>
> // obtain the 'trans_id' values, one by one, and sum() the price
> for($i = 0; $i < $numrecords; $i++) {
>
> $trans_id = pg_Result($result, $i, 0); // record $i, index 0
>
> $subquery = "select sum(price) from second_table " .
> "where trans_id = $trans_id";
> $subresult = dbExec($postgresConnection, $subquery);
>
> // only one record - to my knowledge - can be returned
> $pricesum[$trans_id] = pg_Result($result, 0, 0);
>
> }
>
> Any help you can give will be graciously accepted.....
>
> Thanks,
>
> Bob
--
La risa es la actitud primigenia hacia la vida:
un modo de acercamiento que pervive sólo en
criminales y artistas
-- Oscar Wilde