Question

For pure educational purposes, what should I write instead of * such that I get only one column city_name with a value from either weather.city or city.name, whichever exists?

flav=# select * from weather full outer join cities on weather.city = cities.name;
     city      | temp_lo | temp_hi | prcp |    date    |     name      | location  
---------------+---------+---------+------+------------+---------------+-----------
 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)
 Hayward       |      37 |      54 |      | 1994-11-29 |               | 
               |         |         |      |            | Graz          | (90,-90)

Answer 1

Found it:

SELECT COALESCE(city, name) AS city_name ...