SQL GROUP BY 語句

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GROUP BY 語句可結合一些聚合函數來使用

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GROUP BY 語句

GROUP BY 語句用於結合聚合函數，根據一個或多個列對結果集進行分組。

SQL GROUP BY 語法

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

 

 

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演示數據庫

在本教程中，我們將使用 RUNOOB 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  | 淘寶          | https://www.taobao.com/   | 13    | CN      |
| 3  | 菜鳥教程      | http://www.runoob.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)

 

 

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GROUP BY 簡單應用

統計 access_log 各個 site_id 的訪問量：

實例

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

 

執行以上 SQL 輸出結果如下：

 

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SQL GROUP BY 多表連接

現在我們想要查找每個送貨員配送的訂單數目。

下面的 SQL 語句統計所有網站的訪問的記錄數：

實例

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;

 

執行以上 SQL 輸出結果如下：