Подзапрос для соединения столбца в одной таблице?

Question

здесь это моя структура базы данных: # проблема заключается в извлечении pref_country

OrderLead : 
id lead order time #lead is foreign key to leaddeatail 
1 10  34  null 
2 14  34  null 
3 17  37  null 

leaddetail :       # all pref_country foreign key to Country 
id name pref_country_1 pref_country_2 pref_country_3 
4 rosh   3    4     null 
10 amit   4    2     3 
14 xxx   2    null     null 

Country : 
id name 
2 India 
3 USA 
4 UK 

теперь я хочу всю информацию предпочтительно сублимитами запросов, как:

orderleadid lead_name lead_pref_country orderlead_time # where order = 34 
1    amit   Uk,India,USA  null 
2    xxx   India    null 

я хочу запросить как (подзапрос): # здесь ид и боковая порода

SELECT id,(SELECT group_concat(P.country separator ",") from Country as P, leaddetail as LD where LD.id = orderlead.lead and LD.pref_contry_1 = P.id) as pref country from orderlead where order = 34; 

Answer 1

SELECT 
    OrderLead.id AS orderleadid, 
    leaddetail.name AS lead_name, 
    CONCAT(IFNULL(c1.id,''), IF(c2.id IS NULL,'', CONCAT(',',c2.name)), IF(c3.id IS NULL,'', CONCAT(',',c3.name))) AS lead_pref_country, 
    OrderLead.time AS orderlead_time 
FROM OrderLead 
    INNER JOIN leaddetail ON leaddetail.id=OrderLead.lead 
    LEFT JOIN Country AS c1 ON c1.id=leaddetail.pref_country_1 
    LEFT JOIN Country AS c2 ON c2.id=leaddetail.pref_country_2 
    LEFT JOIN Country AS c3 ON c3.id=leaddetail.pref_country_3 
-- e.g. WHERE OrderLead.order = 34 
-- e.g. WHERE (c1.name='India' OR c2.name='India' OR c3.name='India')