如何在mysql中完全外連接

Question

我已經搜索並且已經花費了很多時間用於此查詢... 我想要的是我需要輸出特定原材料的原材料名稱，而其中一個列爲空。我試過完全的外連接，但我不知道爲什麼phpmyadmin不接受我的查詢我試過幾乎所有我可以。

表：

purchaserequest_tbl

列：purchaserequestID，單編號，rawmaterialID，rawmaterialquantity

rawmaterial_tbl：

列：ID，名稱，類別，單位

這裏是查詢

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..我真的有在這裏

Answer 1

很難如果我理解你，你發佈查詢爲你工作，但並沒有產生預期的結果。全外連接你沒有工作，因爲MySQL不支持全外連接，所以你必須做出2留在爲了得到這個結果的外連接，試試這個：

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' 

如果你只想要那些這是null，在兩個where子句中都加上WHERE rightTable.Column爲null