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使用MySQL中的AVG函数求平均值的教程_MySQL

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Release: 2016-06-01 13:00:33
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MySQL的AVG函数是用来求出各种记录中的字段的平均值。

要了解AVG功能考虑EMPLOYEE_TBL表具有以下记录:

mysql> SELECT * FROM employee_tbl;
+------+------+------------+--------------------+
| id  | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
|  1 | John | 2007-01-24 |        250 |
|  2 | Ram | 2007-05-27 |        220 |
|  3 | Jack | 2007-05-06 |        170 |
|  3 | Jack | 2007-04-06 |        100 |
|  4 | Jill | 2007-04-06 |        220 |
|  5 | Zara | 2007-06-06 |        300 |
|  5 | Zara | 2007-02-06 |        350 |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)

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现在,假设根据上面的表,要计算所有的dialy_typing_pages的平均值,那么可以通过使用下面的命令:

mysql> SELECT AVG(daily_typing_pages)
  -> FROM employee_tbl;
+-------------------------+
| AVG(daily_typing_pages) |
+-------------------------+
|        230.0000 |
+-------------------------+
1 row in set (0.03 sec)

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可以把平均使用GROUP BY子句设置的各种记录。下面的例子将采取平均到一个人的所有相关的记录,每个人的平均页打印纸。

mysql> SELECT name, AVG(daily_typing_pages)
  -> FROM employee_tbl GROUP BY name;
+------+-------------------------+
| name | AVG(daily_typing_pages) |
+------+-------------------------+
| Jack |        135.0000 |
| Jill |        220.0000 |
| John |        250.0000 |
| Ram |        220.0000 |
| Zara |        325.0000 |
+------+-------------------------+
5 rows in set (0.20 sec)

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