如何在MySQL中撤消having子句的组效果？

Question

查询：对于经过超过三架飞机认证的每位飞行员，找到他/她认证的每架飞机的开斋节和最大巡航范围。

查询我写道：

select certified.eid,cruising_range
from certified join employee 
on employee.eid=certified.eid
join aircraft
on certified.aid=aircraft.aid
having count(certified.eid)>3;

输出：

它仅显示一个巡航范围，但 id 10 的飞行员已通过 4架飞机认证。如何获得其他行？

Answer 1

你的问题实际上分为两部分：

1. 找到经过三架以上飞机认证的飞行员

   Dictionary<string,decimal> packageDict= new Dictionary<string,decimal>();
   
   packageDict.AddKeyIfNotExists("demoKey",500);//will add in dictionary
   packageDict.AddKeyIfNotExists("demoKey1", 200);//will add in dictionary
   packageDict.AddKeyIfNotExists("demoKey", 6);//will not add in dictionary
   

2. 查找这些飞机的续航范围

   SELECT eid FROM certified GROUP BY eid HAVING COUNT(*) > 3
   

结合两者：

SELECT eid, cruising_range FROM aircraft JOIN certified USING (aid) ...

Answer 2

使用group by certified.eid。

  

count是一个聚合运算符，只返回一行   （没有分组条款）

select certified.eid,cruising_range
from certified join employee 
on employee.eid=certified.eid
join aircraft
on certified.aid=aircraft.aid
group by certified.eid`
having count(certified.eid)>3;

没有group by aggregate函数只返回一行