@@ -245,25 +245,43 @@ FROM <replaceable>table_reference</replaceable> <optional>, <replaceable>table_r
245245 condition: it takes a Boolean value expression of the same
246246 kind as is used in a <literal>WHERE</> clause. A pair of rows
247247 from <replaceable>T1</> and <replaceable>T2</> match if the
248- <literal>ON</> expression evaluates to true for them .
248+ <literal>ON</> expression evaluates to true.
249249 </para>
250250
251251 <para>
252- <literal>USING</> is a shorthand notation: it takes a
253- comma-separated list of column names, which the joined tables
254- must have in common, and forms a join condition specifying
255- equality of each of these pairs of columns. Furthermore, the
256- output of <literal>JOIN USING</> has one column for each of
257- the equated pairs of input columns, followed by the
258- remaining columns from each table. Thus, <literal>USING (a, b,
259- c)</literal> is equivalent to <literal>ON (t1.a = t2.a AND
260- t1.b = t2.b AND t1.c = t2.c)</literal> with the exception that
261- if <literal>ON</> is used there will be two columns
262- <literal>a</>, <literal>b</>, and <literal>c</> in the result,
263- whereas with <literal>USING</> there will be only one of each
264- (and they will appear first if <command>SELECT *</> is used).
252+ The <literal>USING</> clause allows you to take advantage of
253+ the specific situation where both sides of the join use the
254+ same name for the joining columns. It takes a
255+ comma-separated list of the shared column names
256+ and forms a join using the equals operator. Furthermore, the
257+ output of <literal>JOIN USING</> has one column for each of the
258+ listed columns, followed by the remaining columns from each table.
265259 </para>
266260
261+ <para>The output column difference between <literal>ON</> and
262+ <literal>USING</> when invoking <literal>SELECT *</> is:</para>
263+ <itemizedlist>
264+ <listitem>
265+ <para>
266+ <literal>ON</> - all columns from <replaceable>T1</> followed
267+ by all columns from <replaceable>T2</>
268+ </para>
269+ </listitem>
270+ <listitem>
271+ <para>
272+ <literal>USING</> - all join columns, one copy each
273+ and in the listed order, followed by non-join columns
274+ in <replaceable>T1</> followed by non-join columns in
275+ <replaceable>T2</>
276+ </para>
277+ </listitem>
278+ <listitem>
279+ <para>
280+ Examples provided below
281+ </para>
282+ </listitem>
283+ </itemizedlist>
284+
267285 <para>
268286 <indexterm>
269287 <primary>join</primary>
@@ -281,6 +299,17 @@ FROM <replaceable>table_reference</replaceable> <optional>, <replaceable>table_r
281299 <literal>CROSS JOIN</literal>.
282300 </para>
283301
302+ <note>
303+ <para>
304+ <literal>USING</literal> is reasonably safe from column changes
305+ in the joined relations since only the specific columns mentioned
306+ are considered. <literal>NATURAL</> is considerably more problematic
307+ if you are referring to relations only by name (views and tables)
308+ since any schema changes to either relation that cause a new matching
309+ column name to be present will cause the join to consider that new column.
310+ </para>
311+ </note>
312+
284313 <para>
285314 The possible types of qualified join are:
286315