sum是聚合函数，所有数据库必须有的，mysql也不例外。聚合函数通常要配合group by子句一起使用。例如 select sum(销售数量) as 总销量 from 销售表;select 客户,sum(销售数量) as 单客户小计 from 销售表 group by 客户;
mysql有没有类似sum一样的*=函数
sum是聚合函数，所有数据库必须有的，mysql也不例外。聚合函数通常要配合group by子句一起使用。例如
select sum(销售数量) as 总销量 from 销售表;
select 客户,sum(销售数量) as 单客户小计
from 销售表 group by 客户;2017-04-10
mysql> create table test1(a int);
Query OK, 0 rows affected (0.03 sec)
mysql> insert into test1 values(2);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test1 values(3);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test1 values(4);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test1 values(5);
Query OK, 1 row affected (0.00 sec)
mysql> select power(10,sum(log(10,a))) from test1;
+--------------------------+
| power(10,sum(log(10,a))) |
+--------------------------+
| 119.99999999999996 |
+--------------------------+
1 row in set (0.00 sec)
mysql>2017-05-25
mysql> create table test1(a int);
Query OK, 0 rows affected (0.03 sec)
mysql> insert into test1 values(2);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test1 values(3);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test1 values(4);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test1 values(5);
Query OK, 1 row affected (0.00 sec)
mysql> select power(10,sum(log(10,a))) from test1;
+--------------------------+
| power(10,sum(log(10,a))) |
+--------------------------+
| 119.99999999999996 |
+--------------------------+
1 row in set (0.00 sec)
mysql>2017-05-25
