SQL GROUP BY 语句

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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。

SQL GROUP BY 语法

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

GROUP BY 简单应用

统计 access_log 各个 site_id 的访问量：

实例

SELECT site_id, SUM(access_log.count) AS nums
FROM access_log

GROUP BY site_id;

SQL GROUP BY 多表连接

下面的 SQL 语句统计所有网站的访问的记录数：

实例

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;