mysql中的常用聚集函數

mysql中的常用聚集函數如下：

示例中使用的數據表內容如下：

MariaDB [test]> select * from stu;
+------+----------+-------+
| id   | name     | class |
+------+----------+-------+
|    1 | xiaoming |     2 |
|    1 | liwen    |     2 |
|    3 | xiaobai  |     1 |
+------+----------+-------+
3 rows in set (0.00 sec)

sum()函數

用來返回集合中的所有值的和

MariaDB [test]> select sum(id) from stu;
+---------+
| sum(id) |
+---------+
|       5 |
+---------+
1 row in set (0.00 sec)

max()函數

返回集合中的最大值

MariaDB [test]> select max(class) from stu;
+------------+
| max(class) |
+------------+
|          2 |
+------------+
1 row in set (0.01 sec)

min()函數

返回集合中的最小值

MariaDB [test]> select min(id) from stu;
+---------+
| min(id) |
+---------+
|       1 |
+---------+
1 row in set (0.00 sec)

avg()函數

返回集合中所有數據的平均值

MariaDB [test]> select avg(id) from stu;
+---------+
| avg(id) |
+---------+
|  1.6667 |
+---------+
1 row in set (0.00 sec)

count()函數

返回集合中值的個數

MariaDB [test]> select count(class) from stu;
+--------------+
| count(class) |
+--------------+
|            3 |
+--------------+
1 row in set (0.00 sec)

MariaDB [test]> select count(*) from stu;
+----------+
| count(*) |
+----------+
|        3 |
+----------+
1 row in set (0.00 sec)

這些聚集函數的參數也可以是表達式