From: Tom Lane <tgl@sss.pgh.pa.us>
To: Steve Lau <stevelauc@outlook.com>
cc: "pgsql-docs@postgresql.org" <pgsql-docs@postgresql.org>
Subject: Re: Index of expression over table row or column
In-reply-to: <964FED20-AC2E-47C5-86FB-95C356A68B81@outlook.com>
References: <964FED20-AC2E-47C5-86FB-95C356A68B81@outlook.com>
Comments: In-reply-to Steve Lau <stevelauc@outlook.com>
	message dated "Wed, 16 Oct 2024 03:07:15 -0000"
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Date: Tue, 15 Oct 2024 23:23:08 -0400
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Steve Lau <stevelauc@outlook.com> writes:
> I am reading this documentation[1], and it has a sentence that I don=E2=80=
=99t quite understand: "The index columns (key values) can be either simpl=
e columns of the underlying table or expressions over the table rows.=E2=80=
=9D, I am thinking that for the index of expressions, aren=E2=80=99t those=
 expressions over table column? e.g., =E2=80=9CCREATE INDEX idx_lower_last=
_name ON users(LOWER(last_name))=E2=80=9D, =E2=80=9Clast_name" is a column=
 rather than a row.

Consider

CREATE INDEX idx_lower_name ON users(LOWER(last_name || ' ' || first_name)=
);

			regards, tom lane