Oracle SQL：无效的标识符

Question

谁能向我解释为什么dLoad在GROUP BY行中是无效标识符？ 这在Mysql上运行良好，但我无法使其与Oracle一起使用。

CREATE OR REPLACE VIEW DoctorsLoad AS
    SELECT dID, gender, specialty, 'Overloaded' AS dLoad
    FROM Doctor D, Examine E
    WHERE D.dID = E.doctor_id
    GROUP BY dID, gender, specialty, dLoad
    HAVING COUNT(*) > 10
    UNION
    SELECT dID, gender, specialty, 'Underloaded' AS dLoad
    FROM Doctor D, Examine E
    WHERE D.dID = E.doctor_id
    GROUP BY dID, gender, specialty, dLoad
    HAVING COUNT(*) <= 10;

Answer 1

使用Oracle RDMS，您不能在GROUP BY子句中使用别名，但是对于“重载”之类的文字，无论如何您都无需将其包括在组中。

CREATE OR REPLACE VIEW DoctorsLoad AS
    SELECT dID, gender, specialty, 'Overloaded' AS dLoad
    FROM Doctor D, Examine E
    WHERE D.dID = E.doctor_id
    GROUP BY dID, gender, specialty
    HAVING COUNT(*) > 10
    UNION ALL
    SELECT dID, gender, specialty, 'Underloaded' AS dLoad
    FROM Doctor D, Examine E
    WHERE D.dID = E.doctor_id
    GROUP BY dID, gender, specialty
    HAVING COUNT(*) <= 10;

我还建议使用UNION ALL ，这样可以避免执行过滤操作来删除重复的行。