xacinay xacinay - 4 months ago 9
SQL Question

StoredProc manipulating Temporary table throws 'Invalid column name' on execution

I have a a number of sp's that create a temporary table

#TempData
with various fields. Within these sp's I call some processing sp that operates on
#TempData
. Temp data processing depends on sp input parameters. SP code is:

CREATE PROCEDURE [dbo].[tempdata_proc]
@ID int,
@NeedAvg tinyint = 0
AS
BEGIN
SET NOCOUNT ON;
if @NeedAvg = 1
Update #TempData set AvgValue = 1
Update #TempData set Value = -1;
END


Then, this sp is called in outer sp with the following code:

USE [BN]
--GO
--DBCC FREEPROCCACHE;
GO

Create table #TempData
(
tele_time datetime
, Value float
--, AvgValue float
)
Create clustered index IXTemp on #TempData(tele_time);

insert into #TempData(tele_time, Value ) values( GETDATE(), 50 ); --sample data

declare
@ID int,
@UpdAvg int;
select
@ID = 1000,
@UpdAvg = 1
;

Exec dbo.tempdata_proc @ID, @UpdAvg ;
select * from #TempData;
drop table #TempData


This code throws an error: Msg 207, Level 16, State 1, Procedure tempdata_proc, Line 8: Invalid column name "AvgValue".

But if only I uncomment declaration
AvgValue float
- everything works OK.

The question: is there any workaround letting the stored proc code remain the same and providing a tip to the optimizer - skip this because AvgValue column will not be used by the sp due to params passed.

Dynamic SQL is not a welcomed solution BTW. Using alternative to
#TempData
tablename is undesireable solution according to existing tsql code (huge modifications necessary for that).
Tried SET FMTONLY, tempdb.tempdb.sys.columns, try-catch wrapping without any success.

Answer

The way that stored procedures are processed is split into two parts - one part, checking for syntactical correctness, is performed at the time that the stored procedure is created or altered. The remaining part of compilation is deferred until the point in time at which the store procedure is executed. This is referred to as Deferred Name Resolution and allows a stored procedure to include references to tables (not just limited to temp tables) that do not exist at the point in time that the procedure is created.

Unfortunately, when it comes to the point in time that the procedure is executed, it needs to be able to compile all of the individual statements, and it's at this time that it will discover that the table exists but that the column doesn't - and so at this time, it will generate an error and refuse to run the procedure.

The T-SQL language is unfortunately a very simplistic compiler, and doesn't take runtime control flow into account when attempting to perform the compilation. It doesn't analyse the control flow or attempt to defer the compilation in conditional paths - it just fails the compilation because the column doesn't (at this time) exist.

Unfortunately, there aren't any mechanisms built in to SQL Server to control this behaviour - this is the behaviour you get, and anything that addresses it is going to be perceived as a workaround - as evidenced already by the (valid) suggestions in the comments - the two main ways to deal with it are to use dynamic SQL or to ensure that the temp table always contains all columns required.

One way to workaround your concerns about maintenance if you go down the "all uses of the temp table should have all columns" is to move the column definitions into a separate stored procedure, that can then augment the temporary table with all of the required columns - something like:

create procedure S_TT_Init
as
    alter table #TT add Column1 int not null
    alter table #TT add Column2 varchar(9) null
go
create procedure S_TT_Consumer
as
    insert into #TT(Column1,Column2) values (9,'abc')
go
create procedure S_TT_User
as
    create table #TT (tmp int null)
    exec S_TT_Init
    insert into #TT(Column1) values (8)
    exec S_TT_Consumer
    select Column1 from #TT
go
exec S_TT_User

Which produces the output 8 and 9. You'd put your temp table definition in S_TT_Init, S_TT_Consumer is the inner query that multiple stored procedures call, and S_TT_User is an example of one such stored procedure.

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