Mysql（三）聚集函数

 

1. 平均值AVG()

    SELECT AVG(`level`) AS avg_level FROM `BasicLevel`

2. 计数COUNT()

 a. 使用COUNT(*)计数时，会包含NULL值。

 b. 使用COUNT(column)计数时，不包含null值。

例：SELECT COUNT(*) AS equal_9 FROM `BasicLevel` WHERE `level` = 9

3. MAX

 例：SELECT MAX(`level`) AS max_value FROM `BasicLevel` WHERE `code` = '000001'

4. MIN

 例：SELECT MIN(`level`) AS min_value FROM `BasicLevel` WHERE `code` = '000001'

5. SUM

 例：SELECT SUM(`level`) AS sum_value FROM `BasicLevel` WHERE `code` = '000001'