SQL GROUP BY 语句

    GROUP BY 语句可结合一些聚合函数来使用。

    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。

SQL GROUP BY 语法

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

演示数据库

GROUP BY 简单应用

SELECT site_id, SUM(access_log.count) AS nums
FROM access_log GROUP BY site_id;  //统计各个site_id的访问量

  

SQL GROUP BY 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;