如何用SQL查找双打？

Question

使用Chinook Test Database我写了这个SQL语句来显示两个特定客户订购的所有曲目：

SELECT inv.BillingCity,cus.LastName,tra.Name
        FROM invoice AS inv
        JOIN customer AS cus ON inv.CustomerId=cus.CustomerId
        JOIN invoiceline inl ON inv.InvoiceId=inl.InvoiceId
        JOIN track tra ON tra.TrackId=inl.TrackId
        WHERE cus.LastName IN ('Schneider','Schröder')
        ORDER BY inv.BillingCity,cus.LastName,tra.Name

我发现有一个客户订购了两次跟踪：

我如何编写SQL语句来查找这样的双打，即“返回一位客户多次订购的所有曲目”？

Answer 1

试试这个：

SELECT cus.CustomerId,tra.Name,COUNT(cus.CustomerId) AS tot
       FROM invoice AS inv
       JOIN customer AS cus ON inv.CustomerId=cus.CustomerId
       JOIN invoiceline inl ON inv.InvoiceId=inl.InvoiceId
       JOIN track tra ON tra.TrackId=inl.TrackId
       GROUP BY cus.CustomerId,tra.Name
       HAVING tot > 1