Question

只需要新sql学习者的帮助。

我有两张桌子。产品，供应商。产品具有Vendor_ID作为外键。我需要显示每个供应商的vendor_name，vendor_phone和产品数量。如果你帮我简单解释一下查询，我会很高兴。

Answer 1

您可以使用COUNT(*)执行GROUP BY，如下所示。

SELECT V.VendorId, V.Vendor_Name AS VendorName, V.Vendor_Phone, Count(*) [Count]
FROM Vendor V INNER JOIN Product P ON P.Vendor_ID = V.Vendor_ID 
GROUP BY  V.VendorId, V.Vendor_Name,V.Vendor_Phone

或使用如下的子查询。

SELECT V.Vendor_Name AS VendorName, V.Vendor_Phone,
  (
   SELECT COUNT(*) FROM Product P WHERE P.Vendor_ID = V.Vendor_ID 
  ) AS [Count]
FROM Vendor V

您也可以使用ROW_NUMBER()执行此操作，如下所示。

SELECT * FROM
(
    SELECT V.VendorId, V.Vendor_Name AS VendorName, V.Vendor_Phone, 
            ROW_NUMBER() OVER(PARTITION BY V.Vendor_ID  ORDER BY V.Vendor_ID) RN
            Count(*) OVER(PARTITION BY V.Vendor_ID  ORDER BY V.Vendor_ID) [Count]
    FROM Vendor V INNER JOIN Product P ON P.Vendor_ID = V.Vendor_ID 
) T
WHERE T.RN=1

简单查询新学员

1 个答案: