如何在 SQL 中执行子查询

Question

我的桌子看起来像这样：

如果他们有 SpecialityIdFK = 1 AND SpecialityIdFK= 2，我想检索所有 PractitionerIdFK。我尝试了以下操作，但似乎不起作用。

SELECT PractitionerSpecialities.PractitionerIdFK
FROM PractitionerSpecialities
WHERE PractitionerSpecialities.SpecialityIdFK IN (
        SELECT PractitionerSpecialities.SpecialityIdFK
        FROM PractitionerSpecialities
        WHERE PractitionerSpecialities.SpecialityIdFK = 1
            AND PractitionerSpecialities.SpecialityIdFK = 2
        )

Answer 1

它可以通过在 SQL 中使用IN和BETWEEN运算符来实现。

SELECT  PractitionerSpecialities.PractitionerIdFK 
FROM PractitionerSpecialities
WHERE PractitionerSpecialities.SpecialityIdFK in (1,2)

-- You can BETWEEN Clause as well ..

SELECT  PractitionerSpecialities.PractitionerIdFK 
FROM PractitionerSpecialities
WHERE PractitionerSpecialities.SpecialityIdFK BETWEEN 1 AND 2 

在子查询中使用 OR 运算符而不是 AND 。

Answer 2

您可以使用GROUP BY和HAVING ：

SELECT ps.PractitionerIdFK 
FROM PractitionerSpecialities ps
WHERE ps.SpecialityIdFK IN (1, 2)
GROUP BY ps.PractitionerIdFK 
HAVING COUNT(*) = 2;  -- the size of the comparison list

这假设PractitionerSpecialities中没有重复项。 如果这是可能的，那么使用HAVING COUNT(DISTINCT ps.SpecialityIdFK) = 2 。