我的存储过程返回预期值，但 OUT 参数没有返回任何内容。在程序退出之前打印 out 参数的值，参数的值被设置并且看起来很棒。那么为什么我的测试代码没有得到任何价值呢？
USE MyDB
GO
EXECUTE sp_addmessage
@msgnum = 51001,
@severity = 16,
@msgtext = N'Resource NOT Available',
@lang = 'us_english',
@replace = REPLACE
GO
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[GetNewFileNumber]') AND type in (N'P', N'PC'))
DROP PROCEDURE [dbo].[GetNewFileNumber]
GO
CREATE PROCEDURE dbo.GetNewFileNumber
(
@NextFileNum nvarchar(11) = NULL output
)
AS
BEGIN
set transaction isolation level serializable
begin transaction
declare @LockResult int;
declare @CurrentDate date;
declare @FileNumberDate date;
declare @FileNumber int;
execute @LockResult = sp_getapplock
@Resource = 'GetNewFileNumber_TRANSACTION',
@LockMode = 'Exclusive',
@LockTimeout = 0
if @LockResult <> 0
begin
rollback transaction
raiserror ( 51001, 16, 1 )
return
end
set @CurrentDate = CONVERT (date, GETUTCDATE());
select @FileNumberDate = filedate,
@FileNumber = fileCount from dbo._globalCounters;
if @FileNumberDate != @CurrentDate
begin
set @FileNumberDate = @CurrentDate;
set @FileNumber = 0;
end
set @FileNumber = @FileNumber + 1;
update dbo._globalCounters
set fileDate = @FileNumberDate, fileCount = @FileNumber;
set @NextFileNum = convert(nvarchar(6), @FileNumberDate, 12) +
'-' +
RIGHT('00'+convert(nvarchar(2), @FileNumber),2);
execute sp_releaseapplock 'GetNewFileNumber_TRANSACTION'
commit transaction
print 'filenum:' + @NextFileNum
return @FileNumber;
END
GO
--Test the procedure
DECLARE @return_value int
DECLARE @out_value nvarchar(11)
EXEC @return_value = [dbo].[GetNewFileNumber] @out_value
SELECT 'Return Value' = @return_value, 'Out Value' = @out_value -- Out value always returns null?!
GO