如何從mysql中的子查詢返回零而不是null

Question

我創建了一個查詢，當從子查詢返回null時，我想返回0，我使用了IFNULL函數，但最后仍然得到null。 下面是一個類似的查詢，請幫助，不知道該怎么辦。 （PS：我用手機寫了這個，所以mu格式可能看起來不好，對不起）

SELECT t1.id, t1.Amount, t1.parent, 
      ( SELECT @Total := IFNULL(SUM(t2.amount), 0) AS amount FROM transactions t2 WHERE t1.`id` = t2.parent GROUP BY t2.parent ) AS AmountRepaid, 
      ( SELECT CASE WHEN CAST(SUM(t3.amount) AS DECIMAL) > CAST(t1.amount AS DECIMAL) THEN "Over" WHEN CAST(SUM(t3.amount) AS DECIMAL) = CAST(t1.amount AS DECIMAL) THEN "Complete" ELSE "Incomplete" END FROM transactions t3 WHERE t1.`id` = t3.Parent GROUP BY t3.Parent ) AS PaymentStatus 
      FROM transactions t1 WHERE t1.`Parent` IS NULL;

Answer 1

嘗試使用以下方式：

SELECT t1.id, t1.Amount, t1.parent, 
       @Total := IFNULL( ( SELECT SUM(t2.amount) AS amount FROM transactions t2 WHERE t1.`id` = t2.parent GROUP BY t2.parent ), 0) AS AmountRepaid, 

Answer 2

嘗試這個：

SELECT t1.id, t1.Amount, t1.parent, 
   IF(SUM(t2.amount) IS NULL, 0 ,SUM(t2.amount)) AS amount FROM transactions t2 WHERE t1.`id` = t2.parent GROUP BY t2.parent ) AS AmountRepaid, 
  ( SELECT CASE WHEN CAST(SUM(t3.amount) AS DECIMAL) > CAST(t1.amount AS DECIMAL) THEN "Over" WHEN CAST(SUM(t3.amount) AS DECIMAL) = CAST(t1.amount AS DECIMAL) THEN "Complete" ELSE "Incomplete" END FROM transactions t3 WHERE t1.`id` = t3.Parent GROUP BY t3.Parent ) AS PaymentStatus 
  FROM transactions t1 WHERE t1.`Parent` IS NULL;