在 Access 中创建子查询

Question

我正在尝试在 Access 中创建子查询，但我收到一条错误消息，指出此子查询可以返回一条记录。我想找到拥有最多宠物的前 10 家公司，然后我想知道这些宠物的名字。我以前从未创建过子查询，所以我不确定我哪里出错了。这是我所拥有的：

SELECT TOP 10 dbo_tGovenrnmentRegulatoryAgency.GovernmentRegulatoryAgency
(SELECT dbo_tPet.Pet
FROM dbo_tPet)

FROM dbo_tPet INNER JOIN dbo_tGovenrnmentRegulatoryAgency ON
dbo_tPet.GovernmentRegulatoryAgencyID =
dbo_tGovenrnmentRegulatoryAgency.GovernmentRegulatoryAgencyID
GROUP BY dbo_tGovenrnmentRegulatoryAgency.GovernmentRegulatoryAgency
ORDER BY Count(dbo_tPet.PetID) DESC;

Answer 1

考虑这个解决方案，在WHERE IN () 子句中需要一个子查询：

SELECT t1.GovernmentRegulatoryAgency, dbo_tPet.Pet,
FROM dbo_tPet 
INNER JOIN dbo_tGovenrnmentRegulatoryAgency t1 ON
dbo_tPet.GovernmentRegulatoryAgencyID = t1.GovernmentRegulatoryAgencyID    
WHERE t1.GovernmentRegulatoryAgency IN   
    (SELECT TOP 10 t2.GovernmentRegulatoryAgency
    FROM dbo_tPet 
    INNER JOIN dbo_tGovenrnmentRegulatoryAgency t2 ON
    dbo_tPet.GovernmentRegulatoryAgencyID = t2.GovernmentRegulatoryAgencyID
    GROUP BY t2.GovernmentRegulatoryAgency
    ORDER BY Count(dbo_tPet.Pet) DESC);

不需要表别名，但我将它们包括在内以进行演示。

Answer 2

希望这样做：

SELECT a.GovernmentRegulatoryAgency, t.NumOfPets
FROM dbo_tGovenrnmentRegulatoryAgency a
INNER JOIN (
    SELECT TOP 10 p.GovernmentRegulatoryAgencyID, COUNT(p.PetID) AS NumOfPets
    FROM dbo_tPet p
    GROUP BY p.GovernmentRegulatoryAgencyID
    ORDER BY COUNT(p.PetID) DESC
) t
ON a.GovernmentRegulatoryAgencyID = t.GovernmentRegulatoryAgencyID

简而言之，首先对嵌套查询进行排序，确定相关机构是什么，然后内部连接回机构表以获取所选择的机构的详细信息。