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Date: Tue, 12 May 2009 10:28:57 +0200
Message-ID: <162867790905120128h1dff1ba3mdc9c511af938e595@mail.gmail.com>
Subject: Re: Array: comparing first N elements?
From: Pavel Stehule <pavel.stehule@gmail.com>
To: David Garamond <davidgaramond@gmail.com>
Cc: pgsql-sql@postgresql.org
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Hello

create or replace function eqn(anyarray, anyarray, int)
returns boolean as $$
  select not exists(select $1[i] from generate_series(1,$3) g(i)
                           except
                           select $2[i] from generate_series(1,$3) g(i))
$$ language sql immutable strict;

postgres=3D# select eqn(array[1,2,3,4,5], array[1,2,3,5,6], 3);
 eqn
-----
 t
(1 row)

Time: 1,590 ms
postgres=3D# select eqn(array[1,2,3,4,5], array[1,2,3,5,6], 4);
 eqn
-----
 f
(1 row)

regards
Pavel Stehule

2009/5/12 David Garamond <davidgaramond@gmail.com>:
> I have a "materialized path" tree table like this (simplified):
> CREATE TABLE product (
> =C2=A0 =C2=A0 id SERIAL PRIMARY KEY,
> =C2=A0 =C2=A0 parents INT[] NOT NULL,
> =C2=A0 =C2=A0 name TEXT NOT NULL,
> =C2=A0 =C2=A0 UNIQUE (parents, name)
> );
> CREATE INDEX name ON product(name);
>
> Previously I use TEXT column for parents, but arrays look interesting and
> convenient so I'm considering migrating to arrays. However, how do I rewr=
ite
> this using arrays?
> SELECT * FROM product
> WHERE parents LIKE '0001/0010/%';
> In other words, testing against the first N elements in an array.
> Regards,
> Dave