MySQL常用函数汇总——聚合函数

有数据表如：

mysql> use test_db;
Database changed
mysql> SELECT * FROM tb_students_score;
+--------------+---------------+
| student_name | student_score |
+--------------+---------------+
| Dany         |            90 |
| Green        |            99 |
| Henry        |            95 |
| Jane         |            98 |
| Jim          |            88 |
| John         |            94 |
| Lily         |           100 |
| Susan        |            96 |
| Thomas       |            93 |
| Tom          |            89 |
+--------------+---------------+
10 rows in set (0.13 sec)

1. MAX 查询指定列的最大值

   mysql> SELECT MAX(student_score)
       -> AS max_score
       -> FROM tb_students_score;
   +-----------+
   | max_score |
   +-----------+
   |       100 |
   +-----------+
   1 row in set (0.06 sec)

2. MIN 查询指定列的最小值

   mysql> SELECT MIN(student_score)
       -> AS min_score
       -> FROM tb_students_score;
   +-----------+
   | min_score |
   +-----------+
   |        88 |
   +-----------+
   1 row in set (0.00 sec)

3. COUNT 统计查询结果的行数

   mysql> SELECT COUNT(student_name)
       -> AS students_number
       -> FROM tb_students_score;
   +-----------------+
   | students_number |
   +-----------------+
   |              10 |
   +-----------------+
   1 row in set (0.03 sec)

4. SUM 返回指定列数据的总和

   mysql> SELECT SUM(student_score)
       -> AS score_sum
       -> FROM tb_students_score;
   +-----------+
   | score_sum |
   +-----------+
   |       942 |
   +-----------+
   1 row in set (0.00 sec)

5. AVG 返回指定列数据的平均值

   mysql> SELECT AVG(student_score)
       -> AS score_avg
       -> FROM tb_students_score;
   +-----------+
   | score_avg |
   +-----------+
   |   94.2000 |
   +-----------+
   1 row in set (0.03 sec)