mysql - `Group By` 返回空行

Question

请看下面的代码。

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

“仅”当特定投资组合“至少”有 1 笔交易时，此方法才能正常工作。如果该投资组合根本没有交易，那么它只是返回空行，这意味着什么都没有。

我尝试与 Ongoing_Portfolio.idOngoing_Portfolio、Transactions.idTransactions、Ongoing_Portfolio.idPortfolio 进行分组，但效果并不好。为什么会出现这样的情况？

Answer 1

替换

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

由

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