RE: best way to combine results from two tables


#1

I’m going to throw my .02 in on this one.

I’m a long time DBA, and in my opinion, some things are just better left
to the database as a view (as you stated), a stored procedure, or a
table returning function. There are many many complex data operations
that will occur much faster if run natively on the database.
(Operations that require temp tables, and cubes, etc. come to mind)

At any rate, my guess is that rails would treat a view and a tables the
same way…


From: removed_email_address@domain.invalid
[mailto:removed_email_address@domain.invalid] On Behalf Of Larry W.
Sent: Wednesday, March 08, 2006 5:04 PM
To: removed_email_address@domain.invalid
Subject: Re: [Rails] best way to combine results from two tables

I’ve got the farmer table down :slight_smile:

I’m going to try an implementation that selects from both tables and
merges the results in the controller. In my application, I think I can
do this safely because there’s a limited amount of current data (per
farmer). Also going to try to create a pagination object manually on
the merged data. I’ll let you know how it turns out.

The only alternative i could think of is to merge all the data in a
single table as you suggested, possibly using updatable views to create
models for each of the subtypes, but that seems to add a lot of
overhead.

On 3/8/06, Craig W. removed_email_address@domain.invalid wrote:

OK - in that case, I am definitely interested if someone takes the time
to explain because I am working on reports that need to iterate over a
lot of items in a different manner but similarly enough that I might
learn something useful.

Craig

ps…I still would have a ‘farmers’ table

On Wed, 2006-03-08 at 16:19 -0500, Larry W. wrote:

That might have been best, but the animals are very different. lots of


#2

I was wondering about that (view-table equivalence). Also not sure how
to
create a view that concatenates data from two tables (rather than
joining),
but I posted on the postgresql list for that one.

Since I’m starting to think that rolling my own would mean i can’t get
pagination to work, i will probably try the db way.


#3

You probably want UNION:

create view farm_view as
select ‘cow’ as animal_type, name, age, farmer from cows
union
selec ‘sheep’ as animal_type, name, age, farmer from sheeps
union
selec ‘horse’ as animal_type, name, horse_age as age, farmer from
horses
order by name, age, farmer desc ;


#4

I did it with a union. now i’m going to try to build a model and see
how
rails deals with it.