External table' location

Question

Database Oracle 11g R2 on Sun
I have a common structure on a external table, which will be supplied by multiple source files.
Instead of creating multiple ext table, I have created one and wants to use this one to for all files (FILE NAME is different)
alter table tbl_nm location ('filename1.dat')
And I cannot specify all possible file names, because it failed. At one point of time there will be only one file will be available for this external table.
Is there anyother best practicies for this approach?
Thanks,

Answer 1

Well, SOME sort of processing needs to be done to determine what file to point to!
Another option would be to
1.) Create an external table for each file
2.) Create a function which returns a pipelined table type
3.) In that function test each external table to see which is valid and return that as the pipelined data (or even aggregate several of them through native dynamic SQL if you like)
4.) Base your mapping on the pipelined function as a source.
Technically, this should be possible although I've never attempted it.
Still, I have a question: You say that you do not want to do any external pre-processing, but what control mechanism are you going to use to ensure that one and only one file exists in that directory at any one time, or to indicate that you are done with that file so that it is removed to make way for the next? It seems that some control and interaction needs to be in place for this sort of scenario, so I have to wonder why your design wants to limit leveraging all that these control mechanisms could do to simplify this process.
Cheers,
Mike