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From: Tim Dudgeon <tdudgeon.ml@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Querying with arrays
Date: Thu, 27 Nov 2014 13:09:59 +0000
Message-ID: <547722A7.4040702@gmail.com> (raw)
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I'm considering using arrays to handle managing "lists" of rows (I know 
this may not be the best approach, but bear with me).

I create a table for my lists like this:**

create table lists (
  id SERIAL PRIMARY KEY,
  hits INTEGER[] NOT NULL
);

Then I can insert the results of a query into that table as a new list 
of hits

INSERT INTO lists (hits)
SELECT array_agg(id)
FROM some_table
WHERE ...;

Now the problem part. How to best use that array of primary key values 
to restore the data at a later stage. Conceptually I'm wanting this:

SELECT * from some_table
WHERE id <is in the list of ids in the array in the lists table>;

These both work by are really slow:

SELECT t1.*
FROM some_table t1
WHERE t1.id IN (SELECT unnest(hits) from lists WHERE id = 2);

SELECT t1.*
FROM some_table t1
JOIN lists l ON t1.id = any(l.hits)
WHERE l.id = 2;

Is there an efficient way to do this, or is this a dead end?

Thanks
Tim

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