From: Tom Lane <tgl@sss.pgh.pa.us>
To: Sonny <sonny.chee@gmail.com>
cc: pgsql-sql@postgresql.org
Subject: Re: Odd unfamiliar Postgres SQL syntax
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Comments: In-reply-to Sonny <sonny.chee@gmail.com>
	message dated "Mon, 31 Jul 2017 09:42:12 -0700"
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Date: Mon, 31 Jul 2017 15:03:17 -0400
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Sonny <sonny.chee@gmail.com> writes:
> Can someone help me understand the following SQL?  What does the notation
> (i.keys).n and (i.keys).x mean... as indicated by the <<<=== in the query.

"(i.keys).n" is selecting the column named "n" from the composite-valued
column "i.keys", where "i" is a table alias exposed by the FROM clause.
The reason we don't just write "i.keys.n" is that the SQL standard says
that should mean column "n" in a table "i.keys" exposed by the FROM
clause --- that is, "i" would be a schema name not a table alias, and
"keys" would be a table name not a column name.

			regards, tom lane


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