I have a two tables.
cities - id_city, city_name
properties - id_property, id_city, property_name
I want to display cities.city_name<
I think the following will do it for you, though I haven't tested it. The trick is to get the property counts in one table, and then to left join that table to the cities table, converting NULLs to 0s using the IFNULL function.
SELECT city_name, IFNULL(property_count, 0)
FROM cities
LEFT JOIN
(SELECT id_city, count(*) as property_count
FROM properties
GROUP BY id_city) city_properties
USING (id_city);