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From: Tom Lane <tgl@sss.pgh.pa.us>
To: simonwhite@dciphercomputing.com
cc: pgsql-docs@postgresql.org
Subject: Re: Order of Operations for Update Command
In-reply-to: <20160825152726.15674.18873@wrigleys.postgresql.org>
References: <20160825152726.15674.18873@wrigleys.postgresql.org>
Comments: In-reply-to simonwhite@dciphercomputing.com
	message dated "Thu, 25 Aug 2016 15:27:26 -0000"
Date: Thu, 25 Aug 2016 12:33:01 -0400
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simonwhite@dciphercomputing.com writes:
> Does the Update command update the columns in the order they are listed?

Notionally, they're all done concurrently.  This is embodied in our
docs by defining the update source expressions thus:

	An expression to assign to the column. The expression can use the
	old values of this and other columns in the table.

> Can an updated column's new value be used in the value calculation for a
> subsequent column?

No, see above.

			regards, tom lane


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