Mysql count return Zero if no record found

Question

I have a two tables.

cities - id_city, city_name
properties - id_property, id_city, property_name

I want to display cities.city_name<

Answer 1

The query:

SELECT cities.*, COUNT(properties.id_city) as num
FROM cities
LEFT JOIN properties on cities.id_city=properties.id_city
GROUP BY cities.id_city

should return a 0 count where you want it, although I'm not 100% certain it works that way in MySQL.

Answer 2

Use an outer join:

select cities.city_name, count(properties.id_city)
  from cities left join properties on cities.id_city = properties.id_city
  group by 1

Answer 3

Simple. Use "(Count(*) + 0)". Any null plus 0 will return a number.

Answer 4

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);