MySQL聚合函数

count(*)

表示计算总行数，括号中写星与列名，结果是相同的

select count(*) from user;

max(列)

表示求此列的最大值

select max(age) from user;

+----------+
| max(age) |
+----------+
|       40 |
+----------+
1 row in set (0.00 sec)

min(列)

表示求此列的最小值

select min(age) from user where isdelete is not null;

+----------+
| min(age) |
+----------+
|       18 |
+----------+
1 row in set (0.00 sec)

sum(列)

表示求此列的和

select sum(age) from user;

+----------+
| sum(age) |
+----------+
|      281 |
+----------+
1 row in set (0.00 sec)

avg(列)

表示求此列的平均值

select avg(age) from user;

+----------+
| avg(age) |
+----------+
|  25.5455 |
+----------+
1 row in set (0.01 sec)