sql中查询同一列所有值出现的次数
https://blog.csdn.net/love_java_cc/article/details/52234889
SELECT country as 国家,COUNT(*) as 次数 FROM table3 GROUP BY country
https://blog.csdn.net/love_java_cc/article/details/52234889
SELECT country as 国家,COUNT(*) as 次数 FROM table3 GROUP BY country