[sql]子查詢

參考網址：iT邦幫忙 MySQL: 子查詢

select gov_code,count(player_id) as cc from (select gov_code,player_id from game group by player_id) abc group by gov_code

player可以參加多項比賽。()內的子查詢先把 player_id group 起來變成只有一筆資料，記得()之後便給個名字，讓它變成一個table。