Question

我创建了一个查询，当从子查询返回null时我想返回0，我使用了IFNULL函数，但最后我仍然得到null。下面是一个类似的查询，请帮忙，不知道该怎么做。（PS：我用手机写这个，所以mu形成可能看起来很糟糕，抱歉）

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

尝试使用以下方式：

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

试试这个：

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;

如何从mysql中的子查询返回零而不是null

2 个答案: