如何在mysql中完全外连接

Question

我已经搜索并且已经花费了很多时间用于此查询... 我想要的是我需要输出特定原材料的原材料名称，而其中一个列为空。我试过完全的外连接，但我不知道为什么phpmyadmin不接受我的查询我试过几乎所有我可以。

表：

purchaserequest_tbl

列：purchaserequestID，单编号，rawmaterialID，rawmaterialquantity

rawmaterial_tbl：

列：ID，名称，类别，单位

这里是查询

SELECT `purchaserequest_tbl`.`orderID` AS 'Order No', 
     `rawmaterial_tbl`.`rawMaterialName` AS 'Raw Material Name', 
     `purchaserequest_tbl`.`rawMaterialQty` AS 'Length (inches)' 
FROM `purchaserequest_tbl` 
LEFT OUTER JOIN `rawmaterial_tbl` 
ON `purchaserequest_tbl`.`rawMaterialID` = `rawmaterial_tbl`.`rawMaterialName` 
WHERE `purchaserequest_tbl`.`purchaseRequestStatus` = 'Requested' 

我希望有人能够帮助我..我真的有在这里

Answer 1

很难如果我理解你，你发布查询为你工作，但并没有产生预期的结果。全外连接你没有工作，因为MySQL不支持全外连接，所以你必须做出2留在为了得到这个结果的外连接，试试这个：

SELECT `purchaserequest_tbl`.`orderID` AS 'Order No', 
     `rawmaterial_tbl`.`rawMaterialName` AS 'Raw Material Name', 
     `purchaserequest_tbl`.`rawMaterialQty` AS 'Length (inches)' 
FROM `purchaserequest_tbl` 
LEFT OUTER JOIN `rawmaterial_tbl` 
ON `purchaserequest_tbl`.`rawMaterialID` = `rawmaterial_tbl`.`rawMaterialName` 
WHERE `purchaserequest_tbl`.`purchaseRequestStatus` = 'Requested' 
UNION 
SELECT `purchaserequest_tbl`.`orderID` AS 'Order No', 
     `rawmaterial_tbl`.`rawMaterialName` AS 'Raw Material Name', 
     `purchaserequest_tbl`.`rawMaterialQty` AS 'Length (inches)' 
FROM `rawmaterial_tbl` 
LEFT OUTER JOIN `purchaserequest_tbl` 
ON `purchaserequest_tbl`.`rawMaterialID` = `rawmaterial_tbl`.`rawMaterialName` 
WHERE `purchaserequest_tbl`.`purchaseRequestStatus` = 'Requested' 

如果你只想要那些这是null，在两个where子句中都加上WHERE rightTable.Column为null