嵌套的SQL計數

Question

我有一張兩張表，會員和國家，我想要做的是找到所有沒有會員的國家。我有點失落，這是我最好的猜測，但它不工作：

SELECT CountryID 
FROM Country 
WHERE (SELECT COUNT(MemberID) FROM Member WHERE PrCountryID = CountryID) = 0 

任何幫助將不勝感激。

neojakey

Answer 1

嘗試使用not exists條款：

SELECT C.CountryID 
FROM Country C 
WHERE not exists(SELECT 1 FROM Member M WHERE M.PrCountryID = C.CountryID) 

Answer 2

select countryID from Country C left join member M on C.CountryID=M.CountryID where M.MemberID is null 

Answer 3

在沒有看到表我想你通過左需要像這樣

select * from Country c 
left outer join Member m on m.PrCountryID = c.CountryID 
where m.PrCountryID is null