I need to solve a problem similar to the language one whereby if a
translation in the chosen languange does not exist, the default one should
be selected. My problem is actually picking a price specific to a certain
class if available or a default price otherwise.

So taking a table like:
classitemprice
A50
1A60
B30
C20
2C0








to find the price of item A I could do:

SELECT
`price`
FROM `price_table`
WHERE `item` = '$item' AND (`class` = '$class' OR `class` = '')
ORDER BY `class` DESC
LIMIT 1

so if $item was 'A' $class was '1', I would get 60, otherwise I will get 50.

Or I could do

SELECT
COALESCE(`s`.`price`,`d`.`price`) `price`
FROM `price_table` `d`
LEFT JOIN `price_table` `s` ON `s`.`item` = `d`.`item` AND `s`.`class` =
'$class'
WHERE `d`.`item` = '$item' AND `d`.`class` = ''

My inclination is to go with the LEFT JOIN, but what do others think?