Query EXCEPT di esempio

La tabella CATEGORY nel database TICKIT contiene le seguenti 11 righe:

 catid | catgroup |  catname  |                  catdesc
-------+----------+-----------+--------------------------------------------
   1   | Sports   | MLB       | Major League Baseball
   2   | Sports   | NHL       | National Hockey League
   3   | Sports   | NFL       | National Football League
   4   | Sports   | NBA       | National Basketball Association
   5   | Sports   | MLS       | Major League Soccer
   6   | Shows    | Musicals  | Musical theatre
   7   | Shows    | Plays     | All non-musical theatre
   8   | Shows    | Opera     | All opera and light opera
   9   | Concerts | Pop       | All rock and pop music concerts
  10   | Concerts | Jazz      | All jazz singers and bands
  11   | Concerts | Classical | All symphony, concerto, and choir concerts
(11 rows)

Supponi che una tabella CATEGORY_STAGE (una tabella di gestione temporanea) contenga una riga aggiuntiva:

 catid | catgroup |  catname  |                  catdesc
-------+----------+-----------+--------------------------------------------
1 | Sports   | MLB       | Major League Baseball
2 | Sports   | NHL       | National Hockey League
3 | Sports   | NFL       | National Football League
4 | Sports   | NBA       | National Basketball Association
5 | Sports   | MLS       | Major League Soccer
6 | Shows    | Musicals  | Musical theatre
7 | Shows    | Plays     | All non-musical theatre
8 | Shows    | Opera     | All opera and light opera
9 | Concerts | Pop       | All rock and pop music concerts
10 | Concerts | Jazz      | All jazz singers and bands
11 | Concerts | Classical | All symphony, concerto, and choir concerts
12 | Concerts | Comedy    | All stand up comedy performances
(12 rows)

Restituisce la differenza tra le due tabelle. In altre parole, restituisce le righe che si trovano nella tabella CATEGORY_STAGE ma non nella tabella CATEGORY:

select * from category_stage
except
select * from category;

catid | catgroup | catname |             catdesc
-------+----------+---------+----------------------------------
12 | Concerts | Comedy  | All stand up comedy performances
(1 row)

La seguente query equivalente utilizza il sinonimo MINUS.

select * from category_stage
minus
select * from category;

catid | catgroup | catname |             catdesc
-------+----------+---------+----------------------------------
12 | Concerts | Comedy  | All stand up comedy performances
(1 row)

Se inverti l'ordine delle espressioni SELECT, la query non restituisce alcuna riga.