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Re: SQL tree duplication

From: tv(at)fuzzy(dot)cz
To: "Philippe Lang" <philippe(dot)lang(at)attiksystem(dot)ch>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: SQL tree duplication
Date: 2008-01-24 14:09:09
Message-ID: 23962.217.77.161.17.1201183749.squirrel@mail.fuzzy.cz (view raw or flat)
Thread:
Lists: pgsql-sql
> Hi,
>
> I have the following kind of sql structure, in 3 levels:
>
> -----------------------
> create table documents (
>   id serial,
>   name varchar(50),
>   primary key (id)
> );
>
> create table lines (
>   id serial,
>   name varchar(50),
>   document_id integer,
>   primary key (id),
>   foreign key (document_id) references documents (id)
> );
>
> create table line_details (
>   id serial,
>   name varchar(50),
>   line_id integer,
>   primary key (id),
>   foreign key (line_id) references lines (id)
> );
> -----------------------
>
> I'd like to be able to "duplicate" a document, with all of its lines and
> line details.
>
> Is there any easy way to do that with Postgresql? The only solution I
> can think of at the moment is to loop through all lines and line
> details, and replace foreign keys properly with values fetch with
> "currval". It should work just fine, but I was wondering if some
> advanced features of Postgresql could help in this situation.

You will have to do that in 3 steps (one for each table), but looping may
not be necessary - just use INSERT ... SELECT ... syntax. Something like

INSERT INTO Lines SELECT FROM Lines WHERE document_id = OLD_ID;

But it depends on primary keys in the Lines and Line_details tables - if
the primary keys are composed (and the document_id is part of them) then
there is no problem with duplicities. Otherwise you'll have to solve it
somehow, and looping may be necessary.

Tomas


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