Auto Inc Procedure - Firebird

Hello, my name is Juan and I would like to have a hand to solve this problem:

I have written a Stored Procedure to simulate an autoinc field. It takes two parameters (field and table). Its algorythm is this:
Select the maximum value
if it is null then return 1
else return maximum value+1
When I tried to compile the code below I've received an error message telling me that the character on line 7 (:table) doesn't exist.

Why is this error ocurring?

Thanks for your atention
Juan Pla

/*-------------CODE--------------------------*/
SET TERM ^ ;
CREATE PROCEDURE PK (FIELD VARCHAR(25), TABLE VARCHAR(25))
RETURNS (INC INTEGER)
AS
DECLARE VARIABLE VALUE INTEGER;
begin
SELECT MAX(:FIELD) FROM :TABLE
INTO :VALUE;
if (:VALUE IS NOT NULL) then :INC = :VALUE + 1
ELSE :inc = 1;
suspend;
end
^
SET TERM ; ^

Hi,

A statement (like SELECT ... FROM mytable) needs to be compiled when creating a stored procedure. You cannot replace column names or table names with parameters.

In Firebird 1.5, you can execute dynamic SQL via the EXECUTE STATEMENT statement - check the release notes on how to do this.

Nevertheless, you DO know that you're way of simulating an auto-inc field is very very multi-user unfriendly, right?
Instead, why don't you use Generators?

--
Martijn Tonies
Database Workbench: works with Firebird, MySQL, InterBase and MSSQL Server
Upscene Productions
http://www.upscene.com