Question

我正在尝试获取与每个客户关联的所有行的总和并加入它们。

但是我发现如果不存在任何行，它会完全抛弃客户。

如果总和为零，我更愿意。我将如何实现这一目标。

这是SQL语句：

SELECT 
    Id, DebitSum
FROM
    Customers
JOIN
    (SELECT 
         SUM(Amount) DebitSum, CustomerId
     FROM 
         Purchases
     WHERE 
         Completed IS NULL
     GROUP BY 
         CustomerId) p ON p.CustomerId = Id;

使用SQL Server，如果重要。

Answer 1

只需使用LEFT JOIN：

SELECT c.Id, COALESCE(p.DebitSum, 0)
FROM Customers c LEFT JOIN
     (SELECT SUM(p.Amount) as DebitSum, p.CustomerId
      FROM Purchases p
      WHERE p.Completed IS NULL
      GROUP BY CustomerId
     ) p
     ON p.CustomerId = c.Id;

这通常是在没有子查询的情况下编写的：

SELECT c.Id, COALESCE(SUM(p.Amount), 0) as DebitSum
FROM Customers c LEFT JOIN
     Purchases p
     ON p.CustomerId = c.Id;
WHERE p.Completed IS NULL
GROUP BY c.Id

Answer 2

您可以使用LEFT JOIN：

SELECT Id, COALESCE(DebitSum,0) AS DebitSum
FROM Customers
LEFT JOIN (
            SELECT SUM(Amount) DebitSum, CustomerId
            FROM Purchases
            WHERE Completed IS NULL
            GROUP BY CustomerId
       ) p ON p.CustomerId = Id;

Answer 3

试试这个：

SELECT Id, DebitSum
FROM Customers
LEFT JOIN (
            SELECT SUM(Amount) DebitSum, CustomerId
            FROM Purchases
            WHERE Completed IS NULL
            GROUP BY CustomerId
       ) p ON p.CustomerId = Id;

您正在进行JOIN，这意味着它必须存在于两个表/数据集中。将其更改为LEFT JOIN只需要它在First表中，而不是在LEFT JOIN之后的那个

Answer 4

您也可以仅使用subquery：

select id, (select coalesce(sum(p.Amount), 0) 
            from Purchases p 
            where p.CustomerId  = c.id and p.Completed IS NULL
            ) as DebitSum
from Customers c
group by id;

Answer 5

SELECT SUM(Amount) DebitSum, CustomerId

信息后没有AS？ select sum(amount) as debitsum, customerid

Answer 6

试试这个选择c.Id，COALESCE（p.DebitSum，0）作为DebitSum 来自客户c LEFT JOIN购买p 在c.Id = p.CustomerId 其中p.completed为null

从中选择总和

6 个答案: