`Group By`返回空行

Question

请查看以下代码。

SELECT ongoing_portfolio.*,
    Portfolio.Activation,
    SUM(case when Transaction_TimeStamp <= ongoing_portfolio.`Updated_Date` 
        then Transactions.`Transaction_Amount` ELSE 0 end) AS `Total` 
    FROM Ongoing_Portfolio
    INNER JOIN Portfolio ON Ongoing_Portfolio.idPortfolio = Portfolio.idPortfolio
    INNER JOIN Transactions ON Transactions.`idPortfolio` = Ongoing_Portfolio.idPortfolio
    WHERE ongoing_portfolio.`idPortfolio`= 5        
    GROUP BY Ongoing_Portfolio.`Updated_Date`  DESC LIMIT 4

如果特定portfolio存在“至少”1个事务，则“仅”可以正常工作。如果该组合根本没有任何交易，那么它只返回空行，这意味着什么。

我尝试使用Ongoing_Portfolio.idOngoing_Portfolio，Transactions.idTransactions，Ongoing_Portfolio.idPortfolio进行分组，但一点也不好。为什么会这样发生？

Answer 1

替换

 INNER JOIN Transactions ON Transactions.`idPortfolio` = Ongoing_Portfolio.idPortfolio

通过

 LEFT JOIN Transactions ON Ongoing_Portfolio.idPortfolio = Transactions.`idPortfolio`

Answer 2

尝试使用LEFT JOIN而不是INNER JOIN