加权平均数

这是一个关于如何直接在MySQL中执行此操作的简单示例.您当然需要在子查询上添加一个条件,以便仅获得相关项目的投票而不是所有投票.

mysql> create table votes( vote int);
Query OK, 0 rows affected (0.01 sec)

mysql> insert into votes values (5),(5),(4);
Query OK, 3 row affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from votes;
+------+
| vote |
+------+
|    5 |
|    5 |
|    4 |
+------+
3 rows in set (0.00 sec)

mysql> select vote,count(vote),vote*count(vote) from votes group by vote;
+------+-------------+------------------+
| vote | count(vote) | vote*count(vote) |
+------+-------------+------------------+
|    4 |           1 |                4 |
|    5 |           4 |               20 |
+------+-------------+------------------+
2 rows in set (0.00 sec)

mysql> select sum(vt)/sum(cnt) FROM (select 
count(vote)*count(vote) as cnt,vote*count(vote)*count(vote) 
as vt from votes group by vote) a;
+------------------+
| sum(vt)/sum(cnt) |
+------------------+
|           4.8000 |
+------------------+
1 row in set (0.00 sec)