<programlisting>
SELECT *
FROM weather LEFT OUTER JOIN cities ON (weather.city = cities.name);
+</programlisting>
+<screen>
city | temp_lo | temp_hi | prcp | date | name | location
---------------+---------+---------+------+------------+---------------+-----------
Hayward | 37 | 54 | | 1994-11-29 | |
San Francisco | 46 | 50 | 0.25 | 1994-11-27 | San Francisco | (-194,53)
San Francisco | 43 | 57 | 0 | 1994-11-29 | San Francisco | (-194,53)
(3 rows)
-</programlisting>
+</screen>
This query is called a <firstterm>left outer
join</firstterm> because the table mentioned on the left of the
FROM weather W1, weather W2
WHERE W1.temp_lo < W2.temp_lo
AND W1.temp_hi > W2.temp_hi;
+</programlisting>
+<screen>
city | low | high | city | low | high
---------------+-----+------+---------------+-----+------
San Francisco | 43 | 57 | San Francisco | 46 | 50
Hayward | 37 | 54 | San Francisco | 46 | 50
(2 rows)
-</programlisting>
+</screen>
Here we have relabeled the weather table as <literal>W1</literal> and
<literal>W2</literal> to be able to distinguish the left and right side