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From: Erland Sommarskog <esquel@sommarskog.se>
Newsgroups: comp.databases.ms-sqlserver
Subject: Re: UPDATE FROM
Date: Mon, 19 Jul 2021 20:52:52 +0200
Organization: Erland Sommarskog
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Anton Shepelev (anton.txt@g{oogle}mail.com) writes:
> Question withdrawn. It was an error in my logic, whereas
> the syntax is quite clear. The simplest UPDATED from another
> table does *not* requre that it the table begin updated be
> mentioned in the FROM clause:
> 
>   UPDATE upd_tab
>   SET col = data_tab.col
>   FROM data_tab
>   WHERE data_tab.code = upd_tab.code
> 

Whereas this is legal and produces something, I definitely recommend 
against it. I will have to admit that I don't understand what this is
doing - and I certainly play an SQL expert on TV.