Oracle SQL：無效的標識符

Question

誰能向我解釋為什么dLoad在GROUP BY行中是無效標識符？ 這在Mysql上運行良好，但我無法使其與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子句中使用別名，但是對於“重載”之類的文字，無論如何您都無需將其包括在組中。

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;

我還建議使用UNION ALL ，這樣可以避免執行過濾操作來刪除重復的行。