如何在MySQL中進行完全外部聯接

Question

我已經搜索過並且已經花了很多時間進行此查詢...我要的是我需要在某一列為空的同時輸出特定原材料的原材料名稱。 我已經嘗試了完全外部聯接，但我不知道為什么phpmyadmin不接受我的查詢IVE並嘗試了幾乎所有我能做的事情。

表格：

Purchaserequest_tbl

列：purchaserequestID，orderID，rawmaterialID，rawmaterialquantity

rawmaterial_tbl：

列：ID，名稱，類別，單位

這是查詢

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'

我希望有人能夠幫助我..我真的很難在這里

Answer 1

如果我理解您，則您發布的查詢對您有效，但未給出預期的結果。 完全外部聯接對您不起作用，因為MYSQL不支持完全外部聯接，因此您必須進行2個左外部聯接才能獲得此結果，請嘗試以下操作：

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'

如果只希望它們為空，則在兩個where子句中添加WHERE rightTable.Column為null