Question

我一直在制作一部剧本上遇到困难，希望能够深入了解我做错了什么

问题：

使用相关子查询返回每个供应商的发票，代表供应商最早的发票（具有最早日期的发票）。每行应包括以下四列：供应商名称，发票编号，发票日期和发票总额。

我的脚本：

SELECT DISTINCT Vendor_Name,
    Invoice_number AS OLDEST_INVOICE,
    Invoice_date,
    invoice_total
FROM Vendors v
JOIN Invoices i ON v.vendor_id = i.vendor_id
WHERE invoice_date IN (
        SELECT DISTINCT MIN(invoice_date)
        FROM invoices i
        JOIN vendors v ON i.vendor_id = v.vendor_id
        GROUP BY v.vendor_name
        )
ORDER BY Invoice_Date;

目前，我的代码返回了太多结果，基本上我无法确定invoice_numbers只会在最短的日期返回。

Answer 1

您需要将联接限制为特定供应商的那些发票，并且具有最早的日期... 你不知道发票表是否有代理PK ......如果没有，请尝试：

 SELECT 
    v.Vendor_Name,  
    i.Invoice_number as OLDEST_INVOICE,  
    i.Invoice_date,  
    i.invoice_total  
 FROM Vendors v  
 JOIN Invoices i 
     ON i.vendor_id = v.vendor_id
        And i.invoice_date =
            (Select MIN(invoice_date)
             From Invoices
             Where vendor_id = v.Vendor_Id)  
ORDER BY i.Invoice_Date;

如果发票表有代理PK，请说InvoiceId，那么试试这个：

 SELECT 
    v.Vendor_Name,  
    i.Invoice_number as OLDEST_INVOICE,  
    i.Invoice_date,  
    i.invoice_total  
 FROM Vendors v  
    JOIN Invoices i 
       ON i.InvoiceId = 
          (Select InvoiceId
           From Invoices
           Where vendor_id = v.Vendor_Id
              And Invoice_Date =
                   (Select Min(Invoice_Date)
                    From Invoices
                    vendor_id = v.Vendor_Id))
ORDER BY i.Invoice_Date;

前者仅使用一个子查询，但后者更真实（更清楚地表达）查询意图的意图。

Answer 2

我建议您不要在WHERE子句中使用子查询，而是在内部JOIN中使用派生表。

SELECT
  v.Vendor_Name, 
  i.Invoice_number as OLDEST_INVOICE, 
  i.Invoice_date, 
  i.invoice_total 
FROM Vendors v 
JOIN Invoices i ON v.vendor_id = i.vendor_id 
JOIN (SELECT 
        i2.vendor_id, 
        MIN(i2.invoice_date) AS min_invoice_date
      FROM invoices i2 
      GROUP BY i2.vendor_id) minv 
  ON minv.vendor_id = v.vendor_id 
   AND minv.min_invoice_date = i.invoice_date
ORDER BY i.Invoice_Date;

Answer 3

根据您的平台，可以更简洁地编写（使用分析窗口函数更容易理解）：

http://my.safaribooksonline.com/book/databases/sql/0596004818/sql-functions/sqlnut2-chp-4-sect-3

SQL脚本，与相关的子查询有关

3 个答案: