On 10/8/06, Dirk Jagdmann <[EMAIL PROTECTED]> wrote:
Hello experts,
I have a database that contains three tables:
create table a (
id serial primary key,
... -- some more fields not relevant for my question
);
create table b (
id serial primary key,
... -- some more fields not relevant for my question
);
create table a_b (
a int not null references a,
b int not null references b
);
Tables a and b have already been filled with lots of rows. Now my
application needs to insert the relationship of a to b into table a_b
and is currently doing it with inserts like the following:
insert into a_b(a,b) values(1,100);
insert into a_b(a,b) values(1,200);
insert into a_b(a,b) values(1,54);
insert into a_b(a,b) values(1,4577);
So for a batch of inserts the value of a stays the same, while for by
arbitrary values are inserted. Now I have wondered if PostreSQL offers
a smarter way to insert those values? A solution can contains usage of
some plpgsql code.
It depends on your logic. If you can write a query that selects out the a and b records, there is a smart way:
insert into a_b(a, b)
This is not really smart because you already have the id values - the select may diminish your performance rather than help. But if the select is "smarter" then you don't even need to know what the
b.id values are:
insert into a_b(a, b)
select 1, b.id from b where b.somecolumn = 'somevalue';
Hope this helps.
==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com
http://codeelixir.com
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