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SQL GROUP BY 语句

SQL GROUP BY 语句

日期:2022-07-05

本文字数:220 字 阅读完需:约 2 分钟

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

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

在本教程中,我们将使用 RUNOOB 样本数据库。

下面是选自 "Websites" 表的数据:

1+----+--------------+---------------------------+-------+---------+ 2| id | name | url | alexa | country | 3+----+--------------+---------------------------+-------+---------+ 4| 1 | Google | https://www.google.cm/ | 1 | USA | 5| 2 | 淘宝 | https://www.taobao.com/ | 13 | CN | 6| 3 | http://www.runoob.com/ | 4689 | CN | 7| 4 | 微博 | http://weibo.com/ | 20 | CN | 8| 5 | Facebook | https://www.facebook.com/ | 3 | USA | 9| 7 | stackoverflow | http://stackoverflow.com/ | 0 | IND | 10+----+---------------+---------------------------+-------+---------+

下面是 "access_log" 网站访问记录表的数据:

1mysql> SELECT * FROM access_log; 2+-----+---------+-------+------------+ 3| aid | site_id | count | date | 4+-----+---------+-------+------------+ 5| 1 | 1 | 45 | 2016-05-10 | 6| 2 | 3 | 100 | 2016-05-13 | 7| 3 | 1 | 230 | 2016-05-14 | 8| 4 | 2 | 10 | 2016-05-14 | 9| 5 | 5 | 205 | 2016-05-14 | 10| 6 | 4 | 13 | 2016-05-15 | 11| 7 | 3 | 220 | 2016-05-15 | 12| 8 | 5 | 545 | 2016-05-16 | 13| 9 | 3 | 201 | 2016-05-17 | 14+-----+---------+-------+------------+ 159 rows in set (0.00 sec)

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;

执行以上 SQL 输出结果如下:

![Image 1][]


SQL GROUP BY 多表连接

下面的 SQL 语句统计有记录的网站的记录数量:

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;

执行以上 SQL 输出结果如下:

![Image 1][]

[Image 1]: