如何从SQL Server中传递的参数中选择表和列名？

Question

I have two very similar tables in our database, and I need to write a stored procedure for my Visual Studio 2010 Web Application to read the data from one of these tables given a table number.

Currently, we only have two tables to select from, but I can see this growing to more as this project grows.

This is sort of what I am trying to do, but this code is not correct:

PROCEDURE [dbo].[spGetData]
  @tableID int
AS
BEGIN
SET NOCOUNT ON;
    declare @col1 nvarchar(50), @table nvarchar(50)
    set @col1=case when @tableID=1 then 'SMRequestID' else 'WHRequestID' end
    set @table=case when @tableID=1 then 'SMRequest' else 'WHRequest' end

    select @col1 as 'Request', WorkOrder, PartNumber, Qty, EmployeeID
    from @table
END

Basically, the ColumnName and TableName depend on the @tableID parameter that will be passed in.

How would I go about doing that?

Note: My searches are not turning up anything related, but I am a C# developer and not a database developer. I imagine this has been asked before, it is just I am not using the right keywords.

Answer 1

Although I think Mark is quite correct given the small number of tables and simplicity of your queries, here is a dynamic sql example that passes both the table and column names:

CREATE PROCEDURE spGetData
(
@TableName nvarchar(128),
@ColumnName nvarchar(128)
)
AS
  BEGIN
    SET NOCOUNT ON;
    DECLARE @SQL nvarchar(4000)
    SET @SQL = 'SELECT ' + @ColumnName + ', as Request, WorkOrder, PartNumber, Qty, EmployeeID FROM ' + @TableName 
    EXEC sp_executesql @SQL
  END

You can call it as follows:

exec spGetData 'SMRequest', 'SMRequestID'
exec spGetData 'WHRequest', 'WHRequestID'

Answer 2

One option would be to use a conditional based upon the ID and put the code for a specific table in each section for the table.

I prefer this method to get away from the dynamic sql and allow the database server to get a fighting chance to optimize the thing for speed reasons by precompiling.

NOTE: database servers are pretty bad at string manipulation (create dynamic sql) in general.

EDIT1: EXAMPLE

FOR INSTANCE: THIS SQL

declare @mytest varchar(5)
set @mytest = 'PROCS'

IF @mytest = 'PROCS'
BEGIN /* STORED PROCS */
  SELECT DISTINCT 
    o.name AS ObjectName_StoredProcedure
  FROM sysobjects as o 
  WHERE o.xtype = 'P'
END
ELSE
IF @mytest = 'DEFAULT'
BEGIN
   SELECT DISTINCT 
    o.name AS ObjectName_StoredProcedure
  FROM sysobjects as o 
  WHERE o.xtype = 'D'
END

gives you the store procedure names or the default constraints depending on what you pass to the parameter.

EDIT2: Based on OP code:

CREATE PROCEDURE [dbo].[spGetData]   
  (@tableID int  )
   AS 
  BEGIN
     SET NOCOUNT ON;
     IF @tableID = 1
     BEGIN
       SELECT SMSRequestId AS 'Request',
          WorkOrder, PartNumber, Qty, EmployeeID 
       FROM SMRequest
     END   
     IF @tableID = 2
     BEGIN
       SELECT WHRequestID AS 'Request',
          WorkOrder, PartNumber, Qty, EmployeeID 
       FROM WHRequest
    END
 END

Answer 3

Do it with dynamic SQL:

PROCEDURE [dbo].[spGetData]
  @tableID int
AS
BEGIN
SET NOCOUNT ON;
    declare @col1 nvarchar(50), @table nvarchar(50),  @cmd nvarchar(400)
    set @col1=case when @tableID=1 then 'SMRequestID' else 'WHRequestID' end
    set @table=case when @tableID=1 then 'SMRequest' else 'WHRequest' end


    @cmd = "select " + @col1 + " as 'Request', WorkOrder, PartNumber, Qty, EmployeeID from " + @table

   EXEC(@cmd)

END