SQL HAVING 子句
SQL HAVING 子句
日期:2022-07-05
本文字数:250 字 阅读完需:约 2 分钟
SQL HAVING 子句
HAVING 子句
在 SQL 中增加 HAVING 子句原因是,WHERE 关键字无法与聚合函数一起使用。
HAVING 子句可以让我们筛选分组后的各组数据。
SQL HAVING 语法
SQL HAVING 语法
SELECT column_name , aggregate_function ( column_name ) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function ( column_name ) operator value ;
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)
SQL HAVING 实例
现在我们想要查找总访问量大于 200 的网站。
我们使用下面的 SQL 语句:
实例
SELECT Websites . name , Websites . url , SUM ( access_log . count ) AS nums FROM ( access_log INNER JOIN Websites ON access_log . site_id = Websites . id ) GROUP BY Websites . name HAVING SUM ( access_log . count ) > 200 ;
执行以上 SQL 输出结果如下:
![Image 1][]
现在我们想要查找总访问量大于 200 的网站,并且 alexa 排名小于 200。
我们在 SQL 语句中增加一个普通的 WHERE 子句:
实例
SELECT Websites . name , SUM ( access_log . count ) AS nums FROM Websites INNER JOIN access_log ON Websites . id = access_log . site_id WHERE Websites . alexa < 200 GROUP BY Websites . name HAVING SUM ( access_log . count ) > 200 ;
执行以上 SQL 输出结果如下:
![Image 1][]
[Image 1]: