7.2. Table Expressions suggestion about NATURAL JOIN - Mailing list pgsql-docs

http://www.postgresql.org/docs/9.0/static/queries-table-expressions.html
http://www.postgresql.org/docs/9.0/static/sql-select.html

Respectively:

"Finally, NATURAL is a shorthand form of USING: it forms a USING list
consisting of all column names that appear in both input tables. As
with USING, these columns appear only once in the output table."

and

"NATURAL is shorthand for a USING list that mentions all columns in
the two tables that have the same names."

To make that comprehensive you can add something like: "Note that if
there is no any "shared" column between tables, then NATURAL JOIN acts
like ON TRUE (that is, tables are cross-joined)", because it's not
obvious.

thanks & regards,
greg szpetkowski