Re: Using random() in update produces same random value for all

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Olleg Samoylov <splarv(at)ya(dot)ru>
Cc: "pgsql-general(at)lists(dot)postgresql(dot)org" <pgsql-general(at)lists(dot)postgresql(dot)org>
Subject: Re: Using random() in update produces same random value for all
Date: 2018-01-22 17:16:21
Message-ID: 15531.1516641381@sss.pgh.pa.us
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Olleg Samoylov <splarv(at)ya(dot)ru> writes:
> Looked like random() is "volatile", but in subselect it works like "stable".

The point here is that that's an uncorrelated subselect --- ie, it
contains no outer references --- so it need not be, and is not,
re-evaluated at every outer row.

regards, tom lane

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