From: Tom Lane <tgl@sss.pgh.pa.us>
To: Luis Roberto Weck <luisroberto@siscobra.com.br>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Random function
Date: Tue, 24 Mar 2020 14:33:11 -0400
Message-ID: <23973.1585074791@sss.pgh.pa.us> (raw)
In-Reply-To: <95311e45-95e3-970b-e54f-3a4595d55dbb@siscobra.com.br>
References: <95311e45-95e3-970b-e54f-3a4595d55dbb@siscobra.com.br>
Luis Roberto Weck <luisroberto@siscobra.com.br> writes:
> I am trying to generate some random data using the random() function.
> However, I am getting the same result over mulitiple rows. This is a
> sample of the SQL I am using:
> select (select string_agg(random()::text,';')
> from pg_catalog.generate_series(1,3,1) )
> from generate_series(1,10,1)
The sub-select is independent of the outer select so it's only computed
once, and then you get ten copies of that result. Restructuring the
query, or inserting an artificial dependency on the outer select's data,
would help.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, luisroberto@siscobra.com.br, pgsql-performance@lists.postgresql.org
Subject: Re: Random function
In-Reply-To: <23973.1585074791@sss.pgh.pa.us>
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