Re: Index of expression over table row or column - Mailing list pgsql-docs

Steve Lau <stevelauc@outlook.com> writes:
> I am reading this documentation[1], and it has a sentence that I don’t quite understand: "The index columns (key
values)can be either simple columns of the underlying table or expressions over the table rows.”, I am thinking that
forthe index of expressions, aren’t those expressions over table column? e.g., “CREATE INDEX idx_lower_last_name ON
users(LOWER(last_name))”,“last_name" is a column rather than a row. 

Consider

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

            regards, tom lane