SQL HAVING 子句
HAVING 子句
在SQL 中增加HAVING 子句原因是,WHERE 關鍵字無法與聚合函數一起使用。
HAVING 子句可以讓我們篩選分組後的各組數據。
SQL HAVING 語法
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;
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value;
演示數據庫
在本教程中,我們將使用w3big 樣本數據庫。
下面是選自"Websites" 表的數據:
+----+--------------+---------------------------+-------+---------+ | id | name | url | alexa | country | +----+--------------+---------------------------+-------+---------+ | 1 | Google | https://www.google.cm/ | 1 | USA | | 2 | 淘宝 | https://www.taobao.com/ | 13 | CN | | 3 | 本教程 | http://www.w3big.com/ | 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" 網站訪問記錄表的數據:
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 實例
現在我們想要查找總訪問量大於200 的網站。
我們使用下面的SQL 語句:
實例
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;
INNER JOIN Websites
ON access_log.site_id=Websites.id)
GROUP BY Websites.name
HAVING SUM(access_log.count) > 200;
執行以上SQL 輸出結果如下:
現在我們想要查找總訪問量大於200 的網站,並且alexa 排名小於200。
我們在SQL 語句中增加一個普通的WHERE 子句:
實例
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;
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;
執行以上SQL 輸出結果如下: