mysql concat 列名

Question

嗨，我刚刚开始学习 sql，我希望使用 concat 将列合并为一个列，但没能做到。我可以在没有 concat 的情况下运行代码，但是当我使用 concat 时，它会给我一个错误代码。谁能告诉我我做错了什么？

SELECT CONCAT('A purchase with the purchase ID of' AS "Constraint",
ONLINEPURCHASE.PurchaseID AS "OLID", 'is an online purchase of type' AS "Condition", ONLINEPURCHASE.OnlineType AS "OLType", 'and also a walkin purchase of location' AS "Condition", WALKINPURCHASE.ShopLocation AS "ShopLocation") 
FROM ONLINEPURCHASE JOIN WALKINPURCHASE
    ON ONLINEPURCHASE.PurchaseID = WALKINPURCHASE.PurchaseID
WHERE WALKINPURCHASE.PurchaseID IN (SELECT PurchaseID
        FROM WALKINPURCHASE);

但出现此错误(错误 1583 (42000):调用 native 函数“concat”时参数不正确)

Answer 1

恭喜你开始学习 SQL，它 super 有用!让我尝试消除您的误解。

CONCAT 函数采用一定数量的字符串或列值并将它们连接在一起。无需在其中使用 AS 关键字。

我认为您正在寻找以下内容:

SELECT
  CONCAT(
    'A purchase with the purchase ID of',
    ONLINEPURCHASE.PurchaseID,
    'is an online purchase of type',
    ONLINEPURCHASE.OnlineType,
    'and also a walkin purchase of location',
    WALKINPURCHASE.ShopLocation
  ) AS result
FROM ONLINEPURCHASE JOIN WALKINPURCHASE
  ON ONLINEPURCHASE.PurchaseID = WALKINPURCHASE.PurchaseID
WHERE WALKINPURCHASE.PurchaseID IN
  (SELECT PurchaseID FROM WALKINPURCHASE);

这将创建您在 CONCAT 语句中构建的句子，并将其作为结果集的单列返回。 (我使用 AS 关键字来重命名您构建的列。)

如果您对此有任何疑问，请告诉我。