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SQL HAVING 子句
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SELECT column_name, aggregate_function(column_name)FROM table_nameWHERE column_name operator valueGROUP BY column_nameHAVING 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：+----+--------------+---------------------------+-------+---------+| id | name | url | alexa | country |+----+--------------+---------------------------+-------+---------+| 1 | Google | https:
//www.google.cm/ | 1 | USA || 2 | 淘宝 | https:
//www.taobao.com/ | 13 | CN || 3 | k88.net | http:
//www.k88.net/ | 4689 | CN || 4 | 微博 | http:
//weibo.com/ | 20 | CN || 5 | Facebook | https:
//www.facebook.com/ | 3 | USA || 7 | stackoverflow | http:
//stackoverflow.com/ | 0 | IND |+----+---------------+---------------------------+-------+---------+下面是 "access_log" 网站访问记录表的数据：mysql> SELECT * FROM access_log;+-----+---------+-------+------------+| aid | site_id | count | date |+-----+---------+-------+------------+| 1 | 1 | 45 | 2016-05-10 || 2 | 3 | 100 | 2016-05-13 || 3 | 1 | 230 | 2016-05-14 || 4 | 2 | 10 | 2016-05-14 || 5 | 5 | 205 | 2016-05-14 || 6 | 4 | 13 | 2016-05-15 || 7 | 3 | 220 | 2016-05-15 || 8 | 5 | 545 | 2016-05-16 || 9 | 3 | 201 | 2016-05-17 |+-----+---------+-------+------------+9 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_logINNER JOIN WebsitesONaccess_log.site_id=Websites.id)GROUP BY Websites.nameHAVINGSUM(access_log.count) > 200;执行以上 SQL 输出结果如下：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 FROMWebsitesINNER JOIN access_logON Websites.id=access_log.site_idWHERE Websites.alexa GROUP BY Websites.nameHAVINGSUM(access_log.count) > 200;执行以上 SQL 输出结果如下：
//www.google.cm/ | 1 | USA || 2 | 淘宝 | https:
//www.taobao.com/ | 13 | CN || 3 | k88.net | http:
//www.k88.net/ | 4689 | CN || 4 | 微博 | http:
//weibo.com/ | 20 | CN || 5 | Facebook | https:
//www.facebook.com/ | 3 | USA || 7 | stackoverflow | http:
//stackoverflow.com/ | 0 | IND |+----+---------------+---------------------------+-------+---------+下面是 "access_log" 网站访问记录表的数据：mysql> SELECT * FROM access_log;+-----+---------+-------+------------+| aid | site_id | count | date |+-----+---------+-------+------------+| 1 | 1 | 45 | 2016-05-10 || 2 | 3 | 100 | 2016-05-13 || 3 | 1 | 230 | 2016-05-14 || 4 | 2 | 10 | 2016-05-14 || 5 | 5 | 205 | 2016-05-14 || 6 | 4 | 13 | 2016-05-15 || 7 | 3 | 220 | 2016-05-15 || 8 | 5 | 545 | 2016-05-16 || 9 | 3 | 201 | 2016-05-17 |+-----+---------+-------+------------+9 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_logINNER JOIN WebsitesONaccess_log.site_id=Websites.id)GROUP BY Websites.nameHAVINGSUM(access_log.count) > 200;执行以上 SQL 输出结果如下：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 FROMWebsitesINNER JOIN access_logON Websites.id=access_log.site_idWHERE Websites.alexa GROUP BY Websites.nameHAVINGSUM(access_log.count) > 200;执行以上 SQL 输出结果如下：
SQL HAVING 子句
