mysql 计算字段/字段（百分比）

round( 字段 / 字段 , 保留小数位数)

注意：  COUNT(p.id)/c.sum    计算时，不能使用别名代替，否则报错（全部数学运算都是）

select 
	COUNT(p.id) as package_count,
	c.sum, 
	ROUND(COUNT(p.id)/c.sum,3) as proportion
from t_order o, t_package p, (select COUNT(1) SUM from t_order) c 
where o.package_id = p.id group by p.id order by package_count desc limit 0,4
           

查询结果：

百分比：

concat(字段，'%')  先round计算数值，再拼接 %

select 
	COUNT(p.id) as package_count,
	c.sum, 
	CONCAT(ROUND(COUNT(p.id)/c.sum * 100 ,3),'%') as proportion
from t_order o, t_package p, (select COUNT(1) SUM from t_order) c 
where o.package_id = p.id group by p.id order by package_count desc limit 0,4
           

查询结果：