The following SQL query will result in counting the number of unique countries in your table.

select  count(distinct country)
from    YourTable

What you need is to select the amount of unique countries. This is done by selecting all country entries, which are then grouped so there is only one country entry per country name.
SELECT count(country) from countrytable group by country;
This is basically the same as Andomars answer.

you can use this

SELECT country, COUNT( id ) 
   FROM [table_name] GROUP BY country
   LIMIT 0 , 30

Output :

country count(id) 
---------------------
 US       2            
 Japan    1           
 china    2

从国家/地区表中选择计数（不同的国家/地区）

select count(distinct country) from table1

SELECT count( DISTINCT country )
 FROM table1 c
 WHERE c.item_id = (
 SELECT main_id
 FROM table2
 WHERE main_id = c.item_id )

从[TableName]中选择计数（不同国家/地区）