選擇MySQL月份（）爲空列

Question

有問題要問。當我使用左連接時，即使某行有空值時，我如何列出所有左表以顯示數據？

繼承人我查詢：

SELECT *, SUM(transactions.debit_credit) current_spending 
FROM (`budget`) LEFT JOIN `categories` ON `budget`.`category`=`categories`.`idcategory` 
LEFT JOIN `user_category` ON `budget`.`category`=`user_category`.`idcategory` 
LEFT JOIN `category_transaction` ON `budget`.`category`=`category_transaction`.`idcategory` 
LEFT JOIN `transactions` ON `category_transaction`.`idtransaction`=`transactions`.`idtransaction` 
WHERE `user_category`.`iduser` = '1' 
AND MONTH(transactions.transaction_date) = '11' 
GROUP BY `budget`.`idbudget`; 

當我刪除AND MONTH(transactions.transaction_date) = '11'的查詢工作正常接受它顯示的所有數據，而不只是1個月交易。

幫助??請？？任何想法如何？

Answer 1

您的where子句將您的left join轉換爲inner join，因爲您在連接表的條件下過濾數據。

而是把該條件的on子句中你加入

SELECT *, SUM(transactions.debit_credit) current_spending 
FROM (`budget`) 
LEFT JOIN `categories` ON `budget`.`category`=`categories`.`idcategory` 
LEFT JOIN `user_category` ON `budget`.`category`=`user_category`.`idcategory` 
         AND `user_category`.`iduser` = '1' 
LEFT JOIN `category_transaction` ON `budget`.`category`=`category_transaction`.`idcategory` 
LEFT JOIN `transactions` ON `category_transaction`.`idtransaction`=`transactions`.`idtransaction` 
         AND MONTH(transactions.transaction_date) = '11' 
GROUP BY `budget`.`idbudget`;