报错啦！错误号：1064SQL错误状态：42000错误信息：You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1sql信息：select keyname,kid from keywords where kid in ()
报错啦！错误号：1064SQL错误状态：42000错误信息：You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1sql信息：select qid,title from kidqid where kid in ()
报错啦！错误号：1064SQL错误状态：42000错误信息：You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1sql信息：select kid,keyname FROM keywords where kid in ()

# 变异系数评价股票

## 变异系数越大好 还是越小好

600623 600599 000687 002174

## 什么是变异系数

$$cv = \frac{\sigma}{\mu}$$

## 怎样评价变异系数（cv=标准差/平均值）的好坏？

• 当平均值接近于0的时候，微小的扰动也会对变异系数产生巨大影响，因此造成精确度不足。

• 变异系数无法发展出类似于均值的置信区间的工具。