在delphi中，存储过程的返回值始终为null

Question

我在delphi / sql服务器上遇到了一个小问题。 我有SP

GO
/****** Object:  StoredProcedure [dbo].[sp_adaugaUser]    Script Date: 6/30/2014 12:33:52 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:      <Author,,Name>
-- Create date: <Create Date,,>
-- Description: <Description,,>
-- =============================================
ALTER PROCEDURE [dbo].[sp_adaugaUser]
    -- Add the parameters for the stored procedure here
    @User varchar(50), 
    @Password varchar(32)--,
   -- @errMesaj varchar(50)
AS
BEGIN
declare @sUser varchar(50),
        @sPassword varchar(32),
        @errMesaj varchar(100),
        @exists bit, 
        @exists2 bit;
set @sUser = LTRIM(RTRIM(@User))
set @sPassword = LTRIM(RTRIM(@Password))


    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    select @exists =  COUNT(*) from sys.server_principals where name = @sUser
    select @exists2 = COUNT(*) from sys.database_principals where name = @sUser
    -- Insert statements for procedure here
    if @exists = 1 begin 
         if @exists2 = 1 set @errMesaj = 1 --'Userul deja exista'  
              else begin 
               exec ('CREATE USER [' + @sUser + '] FOR LOGIN [' + @sUser + ']') 
               set @errMesaj = 2  --'S-a creat userul pentru login deja existent'
               end
                   end
          else begin
                         exec(' CREATE LOGIN [' + @sUser  + '] WITH PASSWORD = ''' +@sPassword + '''
                                 CREATE USER [' + @sUser + '] FOR LOGIN [' +  @sUser+']')
                        set @errMesaj = 3 --'S-a creat user si login'
                        end

 RETURN @errMesaj   
END

该SP将登录名和用户添加到服务器/数据库中...，并根据完成的操作返回一条消息。

在delphi中，我有一个TADOStoredProcedure，它具有3个参数：

1：@User-ftString，pdInput 2：@Password-ftString，pdInput 1：@errMesaj-ftString，pdReturnValue

我这样称呼TADOStoredProcedure：

procedure TdataModule1.AdaugaUser(user, password : string );  // procedura ce apeleaza o SP din BD pentru adaugarea de useri
begin
   sp_adaugaUser.Parameters.ParamByName('@User').Value := user;
   sp_adaugaUser.Parameters.ParamByName('@Password').Value := password;
   sp_adaugaUser.Prepared :=  true ;
   try
   sp_adaugaUser.ExecProc;
   finally
   sp_adaugaUser.Prepared :=  false ;
   sp_vizualizare_useri.Close;
   sp_vizualizare_useri.Open;
   test := sp_adaugaUser.Parameters.ParamByName('@errMesaj').Value;
   end;

end;

但是由于某些原因，当我调试test的值始终为null ，为什么呢？

错误：

Answer 1

如果要按说明使用参数@errMesaj，则必须使用OUTPUT进行定义。

ALTER PROCEDURE [dbo].[sp_adaugaUser]
    -- Add the parameters for the stored procedure here
    @User varchar(50), 
    @Password varchar(32),
    @errMesaj varchar(100) OUTPUT
AS

SQLServer过程的RESULT值限制为整数从存储过程返回的数据

显示不同可能性的示例如下所示：

Alter PROCEDURE [dbo].[sp_adaugaUser]
    -- Add the parameters for the stored procedure here
    @User varchar(50), 
    @Password varchar(32),
    @errMesaj varchar(100) OUTPUT
AS
BEGIN
declare @sUser varchar(50),
        @sPassword varchar(32),
        @ReturnCode int,   
        @exists bit, 
        @exists2 bit;
set @sUser = LTRIM(RTRIM(@User))
set @sPassword = LTRIM(RTRIM(@Password))


    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    select @exists =  COUNT(*) from sys.server_principals where name = @sUser
    select @exists2 = COUNT(*) from sys.database_principals where name = @sUser
    -- Insert statements for procedure here
    if @exists = 1 begin 
         if @exists2 = 1 
            begin
              set @errMesaj = 'Userul deja exista'  
              set @ReturnCode = 1
            end
              else begin 
               exec ('CREATE USER [' + @sUser + '] FOR LOGIN [' + @sUser + ']') 
                 set @errMesaj = 'S-a creat userul pentru login deja existent'
                 set @ReturnCode = 2
               end
                   end
          else begin
                        exec(' CREATE LOGIN [' + @sUser  + '] WITH PASSWORD = ''' +@sPassword + '''
                                 CREATE USER [' + @sUser + '] FOR LOGIN [' +  @sUser+']')
                        set @errMesaj = 'S-a creat user si login'
                        set @ReturnCode = 2
                        end

    Return @ReturnCode
END

通话的最小delphi代码

   sp_adaugaUser.Parameters.ParamByName('@User').Value := user;
   sp_adaugaUser.Parameters.ParamByName('@Password').Value := password;
   sp_adaugaUser.ExecProc;
   Showmessage(sp_adaugaUser.Parameters.ParamByName('@errMesaj').Value);
   Showmessage(IntToStr(sp_adaugaUser.Parameters.ParamByName('@RETURN_VALUE').Value));

将TAdoStoredProc用于sp_adaugaUser您的参数应如下所示

您得到的错误是因为在test := sp_adaugaUser.Parameters.ParamByName('@errMesaj').Value; 值为NULL，无法将其转换为字符串。