Question

SELECT VendorName, COUNT(*) as Total_Invoices
FROM   Invoices JOIN Vendors ON Invoices.VendorID = Vendors.VendorID
WHERE  Vendors.VendorName = 'IBM'
GROUP BY VendorName
ORDER BY Total_Invoices DESC

会出现

VendorName  Total_Invoices
IBM                2

我想这样做只是说

Total_Invoices
     2

未显示IBM VendorName，但仍在计算IBM的总发票

Answer 1

您可以安全地删除此案例中的VendorName。

SELECT COUNT(*) as Total_Invoices
FROM   Invoices JOIN Vendors ON Invoices.VendorID = Vendors.VendorID
WHERE  Vendors.VendorName = 'IBM'
GROUP BY VendorName
ORDER BY Total_Invoices DESC

另一方面，

select也称为投影。你可以安全地删除它而不会造成任何伤害。但是在GROUP BY子句中删除它是一个非常不同的事情。

Answer 2

您只需清除VendorName中的Select即可。在这种情况下，您无需使用GROUP BY或ORDER BY

SELECT COUNT(*) as Total_Invoices
FROM   Invoices JOIN Vendors ON Invoices.VendorID = Vendors.VendorID
WHERE  Vendors.VendorName = 'IBM'

Answer 3

从SELECT中删除VendorName。

在SQL中删除一列

3 个答案: