AVG()

平均值，改函数必须配合表来操作

  1. mysql> SELECT AVG(age) FROM user;
  2. +----------+
  3. | AVG(age) |
  4. +----------+
  5. |  17.0000 |
  6. +----------+

COUNT()

计数，统计表里面有多少数据

  1. mysql> SELECT COUNT(id) FROM user;
  2. +-----------+
  3. | COUNT(id) |
  4. +-----------+
  5. |         7 |
  6. +-----------+

MAX()

最大值

  1. mysql> SELECT MAX(age) FROM user;
  2. +----------+
  3. | MAX(age) |
  4. +----------+
  5. |       21 |
  6. +----------+
  7. -- 如果要查询年级最大人的名字，必须使用子查询的方式查找。
  8. -- 思路 获取所有数据 = （age = 最大值的）
  9. mysql> SELECT * FROM user WHERE age=(SELECT MAX(age) FROM user);
  10. +----+--------+------+------+
  11. | id | name   | age  | sex  |
  12. +----+--------+------+------+
  13. |  4 | 小白   |   21 |      |
  14. +----+--------+------+------+

MIN()

最小值

  1. mysql> SELECT MIN(age) FROM user;
  2. +----------+
  3. | MIN(age) |
  4. +----------+
  5. |       11 |
  6. +----------+

SUM()

求和

  1. mysql> SELECT SUM(age) FROM user;
  2. +----------+
  3. | SUM(age) |
  4. +----------+
  5. |      102 |
  6. +----------+