Question

我正在尝试重写不使用相关查询的SQL查询。这是查询：

SELECT  DISTINCT v.vendor_name, i.invoice_number, 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)

我尝试了很多方法，但我总是遇到这个问题：我不知道如何在此结果集中集成invoice_number和invoice_total列。

SELECT  vendor_name, MIN(invoice_date) 
FROM  vendors JOIN invoices USING (vendor_id)
GROUP BY vendor_name

有人可以帮助我吗？

Answer 1

一种方法是使用分析函数rank

SELECT DISTINCT vendor_name, invoice_number, invoice_date, invoice_total 
  FROM (SELECT v.vendor_name, 
               i.invoice_number, 
               i.invoice_date, 
               i.invoice_total,
               rank() over (partition by v.vendor_id
                                order by i.invoice_date asc) rnk
          FROM vendors v 
               JOIN invoices i 
                 ON i.vendor_id = v.vendor_id)
 WHERE rnk = 1

如果您希望提高查询的效果，我强烈质疑您是否需要DISTINCT，因为这会强制进行额外排序。通常，当开发人员真正错过某些连接条件时，会使用DISTINCT来正确消除重复的行。

编写不使用相关查询的SQL查询

1 个答案: