刪除行時，子查詢返回null

Question

選擇執行後，我收到了錯誤「未知列‘點’在‘where子句’

如何從包含空外部查詢中刪除行記錄從子查詢返回？（我需要使用子查詢，因爲我有需要運行到返回結果子查詢的另一幫我後）

SELECT 
    s.student_name_first, 
    s.student_name_last, 
    (
    SELECT sum(i.points) 
    FROM incidents i 
    WHERE i.student = s.id 
    ) AS points 
FROM students s 
WHERE points IS NOT NULL 
GROUP BY s.id 

我也曾嘗試，結果相同

SELECT 
    s.student_name_first, 
    s.student_name_last, 
    (
    SELECT sum(i.points) AS points 
    FROM incidents i 
    WHERE i.student = s.id AND points IS NOT NULL 
    ) AS p 
FROM students s 
GROUP BY s.id 

在此先感謝

---

解決方案：

我一直在尋找的是HAVING

SELECT 
    s.student_name_first, 
    s.student_name_last, 
    (
    SELECT COALESCE(sum(i.incident_points),0) 
    FROM incidents i 
    WHERE i.student = s.id 
    ) as points 
FROM students s 
GROUP BY s.id 
HAVING points > 0 

Answer 1

的問題是，你不能WHERE子句中使用別名SELECT，他們必須在HAVING。

但是，如果您使用內部聯接，您將不會首先獲得任何空行。

SELECT s.student_name_first, 
     s.student_name_last, 
     SUM(i.points) AS points 
FROM students s 
JOIN incidents i 
ON i.student = s.id 
GROUP BY s.id