它是 SQL SERVER 错误吗？

Question

我似乎无法弄清楚这个 SQL 标量函数发生了什么。我想知道这是否是我遇到的某种错误，因为 select 语句在函数中返回 NULL，而它在函数外工作得很好，或者当 DESC 子句被省略时。

ALTER FUNCTION [dbo].[getInvoiceNumbers]
(

@vatable bit

)
RETURNS nvarchar(20)
AS
BEGIN

DECLARE @latestNonVATInvNumber nvarchar(20), 
        @latestVATInvNumber nvarchar(20), @invoiceNumber nvarchar(20)

if @vatable = 'true'
    begin    
        select TOP 1 @latestVATInvNumber = invoiceNumber from dbo.Invoices where vatable = 'true' ORDER BY invoiceID desc 

        /* remove 'B' from invoice number and convert to int from string */

        set @latestVATInvNumber = cast(substring(@latestVATInvNumber,2,len(@latestVATInvNumber)) as int) + 1

        /* Add 'B' to receipt number with leading zeros so that it is 7 digits including 'B' */

        set @latestVATInvNumber  = 'B' + RIGHT('000000'+ CAST(@latestVATInvNumber AS VARCHAR(6)),6)

        set @invoiceNumber = @latestVATInvNumber
    end
else
    begin

        select TOP 1 @latestNonVATInvNumber = invoiceNumber from dbo.Invoices where vatable = (select cast ('False' as bit)) ORDER BY invoiceID desc


        /* Invoice Number is numeric (non VAT) hence only incrementing it by 1 */

        set @latestNonVATInvNumber = cast(cast(@latestNonVATInvNumber as int) + 1 as nvarchar(10))                                                                                                                                                                                                                                                                                                       

        set @invoiceNumber = @latestNonVATInvNumber
    end

-- Return the result of the function
RETURN @invoiceNumber 

END

给出NULL的部分是这段代码：

select TOP 1 @latestNonVATInvNumber = invoiceNumber from dbo.Invoices where vatable = (select cast ('False' as bit)) ORDER BY invoiceID desc

和

 select TOP 1 @latestVATInvNumber = invoiceNumber from dbo.Invoices where vatable = 'true' ORDER BY invoiceID desc 

如果我删除了“DESC”，那么它会给我来自数据库的结果，或者即使插入了“ASC”，但如果在表。

有什么建议吗？

Answer 1

建议一（不正确）：

第一次查询表时，使用以下过滤器：

where vatable = 'true'

第二次查询时，使用以下内容：

(select cast ('False' as bit))

通过删除 CAST 并使用 where vatable = 'false' 将它们更改为相互匹配。

建议二（答案）：

将AND InvoiceNumber IS NOT NULL 添加到您的条件中

Answer 2

如果您返回超过 1 行，则使用 TOP 1，然后更改返回结果的顺序可能会更改返回给您的 @latestNonVATInvNumber 变量的输出。

我的建议是测试前 1 部分并尝试选择 COUNT(*) 以查看返回的行数。

例如

select COUNT(*) from dbo.Invoices where vatable = (select cast ('False' as bit)) ORDER BY invoiceID desc

然后你可以用类似的东西测试返回什么数据

select * from dbo.Invoices where vatable = (select cast ('False' as bit)) ORDER BY invoiceID desc

也许那样会更清楚为什么会出现 NULL。