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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Wells Oliver <wells.oliver@gmail.com>
Cc: Craig James <cjames@emolecules.com>
Cc: pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: Query planning around one key of a multi-column index
Date: Thu, 19 Dec 2019 00:47:09 -0500
Message-ID: <18012.1576734429@sss.pgh.pa.us> (raw)
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	<CAOC+FBWzn-TK99tZNP4s=HkFk1qWr6QXGnqDarLCKrBK5g_tXA@mail.gmail.com>

Wells Oliver <wells.oliver@gmail.com> writes:
> Is it really always true that querying off any column that's not the first
> column of a multi-column index will NOT use that index?

Nope.  The planner will consider that, though in most cases it's likely
to estimate that there's no benefit to using the index in such cases.
Try reading the *actual* docs, not some third-party site:

https://www.postgresql.org/docs/current/indexes-multicolumn.html

			regards, tom lane

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