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;

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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:

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

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