Question

当两者在自己的select语句中都有自己的别名和表引用时，如何加入A.ID_Number和B.ID_Number？最后一行目前不正确，我需要知道如何解决这个问题。

SELECT*FROM
(SELECT b.ID_Number, b.Price, s.Quantity FROM tbl_bills b
 LEFT JOIN tbl_stock s ON b.Price = s.Price)
AS X

LEFT JOIN

(SELECT c.ID_Number, c.Currency, p.Purchased FROM tbl_currency c
WHERE blahblahblah)
AS Y

ON X.b.ID_Number = Y.c.ID_Number

可能有更好的方法来完成整个语句，但我只想知道如何正确地执行最后一行，因为我的实际查询很多，更长。

编辑：问题解决了。

Answer 1

您必须取消b.和c.：

ON X.ID_Number = Y.ID_Number

Answer 2

主查询看不到子查询中的表名和别名。只需参考列名称。

ON X.ID_Number = Y.ID_Number

Answer 3

您只使用您定义的别名。。。 X和Y。以下是整个查询中的示例：

SELECT x.ID_Number, x.Price, x.Quantity, y.ID_Number, y.Currency, y.Purchased
FROM (SELECT b.ID_Number, b.Price, s.Quantity
      FROM tbl_bills b LEFT JOIN
           tbl_stock s
           ON b.Price = s.Price
     ) X LEFT JOIN
     (SELECT c.ID_Number, c.Currency, p.Purchased
      FROM tbl_currency c
      WHERE blahblahblah
     ) Y
     ON X.ID_Number = Y.ID_Number;

请注意，p.purchased仍有与无法识别的列名相同的错误。

对我来说，这是编写查询的愚蠢方式。我会改用：

SELECT b.ID_Number, b.Price, s.Quantity, c.Currency, p.Purchased  -- c.ID_Number, is not needed unless you want to see if there is a match
FROM tbl_bills b LEFT JOIN
     tbl_stock s
     ON b.Price = s.Price LEFT JOIN
     tbl_currency c
     ON b.ID_Number = c.ID_Number AND blahblahblah;

这更短，更容易编写，更易于阅读，并且应该具有更好的性能，不会实现子查询。

Answer 4

我会这样做：

SELECT b.ID_Number, b.Price, s.Quantity, c.Currency
FROM tbl_bills b
    LEFT JOIN tbl_stock s USING (Price)
    LEFT JOIN tbl_currency c
        ON c.ID_Number = b.ID_Number AND { other criteria goes here }

要获得更具体的信息，您需要发布实际查询。

要解决您的更新＆＃34;如果我尝试X.ID_Number = Y.ID_Number，我会收到错误＆＃34;未知栏＆＃39; X.ID_Number in＆＃39; on子句＆＃39;＆＃34; - 唯一的原因是您的实际查询与您发布的查询不同。人们根据您发布的代码提供答案。在两个子查询中选择ID_Number非常重要，加入将起作用。

MySQL - 加入两个在其中包含别名和连接的SELECT语句

4 个答案: