GROUP BY 语句

GROUP BY 语句用于结合聚合函数，根据一个或多个列对结果集进行分组

GROUP BY 语法

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;

例句：

每个学生的总分数

select S,sum(score) sum from sc group by S

多表连接
SELECT Websites.name,COUNT(access_log.aid) AS nums FROM access_log
LEFT JOIN Websites
ON access_log.site_id=Websites.id
GROUP BY Websites.name;