Question

我开始学习SQL，我坚持这个问题

如果我有这两个表：

行星（名称，大小）

Moon（姓名，PlanetName *）

如何删除超过3个卫星的行星？我不确定我的回答是否正确

DELETE Name
FROM Planet
INNER JOIN Moon WHERE Moon >3

Answer 1

你的答案不正确。具有三个以上卫星的行星由下式给出：

select planetname
from moon
group by panetname
having count(*) > 3;

然后，您可以使用in或exists

删除行星

delete from planet
    where planetname in (select planetname
                         from moon
                         group by planetname
                         having count(*) > 3
                        );

Answer 2

delete from planets where 
    (select count(*) from moon where moon.planetname = planet.name) > 3

或

delete from planets where 
    exists(select count(*) from moon 
           where moon.planetname = planet.name 
           group by planetname  -- you may not need that, because for each row they are all equal, due to the where condition
           having count(*) > 3
          )

Answer 3

您的查询错误！因为你的查询没有提到计数。

尝试此查询

DELETE from planets
     WHERE
       Name = ((SELECT   COUNT(*)  
                FROM     moon 
                WHERE    moon.planetname = planet.name) > 3 )

如何从具有特殊条件的另一个表中删除表中的行？

3 个答案: