Question

select title, Forename AS "Firstname", Surname AS "Lastname", COUNT 
(VISIT.Vet_Id) AS "Visits"
from VISIT, VET
where VISIT.Vet_Id = VET.Vet_Id
group by title, Surname,VISIT.VET_Id
order by title, Surname, VISIT.VET_Id;

当执行上面的代码时，我收到一条错误消息：虽然当我删除Forename AS＆＃34; Firstname＆＃34;

时它不是GROUP BY表达式

为什么会这样？

Answer 1

只需在SELECT中的GROUP BY中添加非汇总列：

select title, Forename AS "Firstname", Surname AS "Lastname",
       COUNT(vi.Vet_Id) AS "Visits"
from VISIT vi join
     VET v
     on vi.Vet_Id = v.Vet_Id
group by title, Forename, Surname
order by title, Forename, Surname;

并且从不在FROM子句中使用逗号。始终使用正确的，明确的JOIN语法。您还应该对所有列引用进行限定。

Answer 2

对于Oracle数据库，我们必须在我们在Select子句中使用的Group by子句中添加所有非聚合字段，否则会出错。在mysql的情况下，group by子句没有这样的限制。

Oracle错误消息：在添加另一个＆＃39;选择＆＃39;时不是GROUP BY表达式条款

2 个答案: