Question

编辑：

对不起，我没有在开始时澄清。 CompanyType为smallint，不为null，TotalLicenses为int，null

基本上我只想查看TotalLicenses > 0 if C.CompanyType != 4

我查看了一些参考指南和教程，但是在这个例子中我找不到确认我正在使用CASE的方法。

当Expiration大于或等于Today的日期时，我试图将“已购买”列更新为1，DemoLicense等于0，如果公司类型不是4，则TotalLicenses大于0。如果是4它可以是0

update WebCatalog.Published.DemoTracking
set Purchased = 1
from WebCatalog.Published.Company C
    inner join WebCatalog.Published.RCompany RC
        on C.RCompany = RC.Link
    inner join WebCatalog.Published.DemoTracking DT
        on C.PKey = DT.CompanyPKey and DT.Purchased = 0
where RC.Expiration >= Cast(GETDATE() as Date) and RC.DemoLicense = 0
and C.TotalLicenses > 
    Case 
        when C.CompanyType != 4 THEN 0
    END

Answer 1

我想你想要：

and ( C.CompanyType <> 4 AND C.TotalLicenses > 0 
   OR C.CompanyType = 4 AND C.TotalLicenses >= 0
    )

可以简化（假设这两列不可为空）到：

and ( C.TotalLicenses > 0 
   OR C.CompanyType = 4 AND C.TotalLicenses = 0
    )

，如果Company.TotalLicenses永远不会有负值，可以进一步简化为：

and ( C.TotalLicenses > 0 
   OR C.CompanyType = 4
    )

Answer 2

我认为案例结构在不同的DBMS之间有所不同。因此以下内容可能不适用于您。

2nd当你没有指定Else时，case返回NULL。与NULL的比较也是NULL，因此不会返回该行。这意味着您需要一个默认案例。

所以你应该写一下：

and C.TotalLicenses > 
    Case 
        when C.CompanyType != 4 THEN 0
        else -1
    END

Answer 3

与你所描述的方式没有多大区别：

update WebCatalog.Published.DemoTracking
set Purchased = 1
from WebCatalog.Published.Company C
        inner join WebCatalog.Published.RCompany RC
            on C.RCompany = RC.Link
        inner join WebCatalog.Published.DemoTracking DT
            on C.PKey = DT.CompanyPKey and DT.Purchased = 0
 where RC.Expiration >= Cast(GETDATE() as Date) and RC.DemoLicense = 0
 and (C.TotalLicenses > 0 or C.CompanyType = 4)

我正确使用CASE吗？

3 个答案: