Question

我正在尝试显示一些合并4个表的信息。我的表是device，device_model，sub_product_area和borrow_device。我遇到的问题是，当我使用LEFT JOIN将表链接到设备表时，来自borrow_device表的transaction_ID有一些重复。所以我想在transaction_Mode上为ORFT JOIN进行ORDER BY，并且只选择＆＃39; red＆＃39;在这种情况下，颜色相关的transaction_ID。我尝试过SELECT DISTINCT，但它没有用。没有类似的问题答案有效。

这是我的查询 - ＆gt;

SELECT * 
FROM device b 
LEFT OUTER JOIN device_model a ON (b.`model_ID`=a.`model_ID`) 
LEFT JOIN sub_product_area c ON (b.`sub_Product_Area_ID` = c.`sub_Product_Area_ID`) 
LEFT JOIN borrow_device d ON (d.`device_ID` = b.`device_ID` and CURDATE() between from_Date and to_Date) 
ORDER BY d.transaction_Mode DESC

My table structures are as below -:

提前致谢！

Answer 1

device表和sub_product_area表有2个字段相关的是sub_product_area_id和product_area_id。在您的SQl语句中尝试添加“and b.product_Area_ID = c.product_Area_ID”，因此您的语法将如下所示：

SELECT * 
FROM device b 
LEFT OUTER JOIN device_model a ON (b.`model_ID`=a.`model_ID`) 
LEFT JOIN sub_product_area c ON (b.`sub_Product_Area_ID` = c.`sub_Product_Area_ID` and b.`product_Area_ID` = c.`product_Area_ID`) 
LEFT JOIN borrow_device d ON (d.`device_ID` = b.`device_ID` and CURDATE() between from_Date and to_Date) 
ORDER BY d.transaction_Mode DESC

Answer 2

在最后添加'GROUP BY'解决了我的问题。谢谢大家！

在My SQL中删除多个JOIN结果中的一个表的重复项

2 个答案: