use of hash files

shivan · Post by **shivan** » Thu Aug 04, 2005 11:46 am

hi,
i m new to datastage. i was going through the documentation but couldnt find what is the real use of hash files. The only thing i understand is that it uses hashing algorithm to feed the rows.

shivan

diamondabhi · Post by **diamondabhi** » Thu Aug 04, 2005 12:37 pm

Hi Shivan,
Hash Files can be used for manythingd, search for Hash Files and u will find a lot of information about it.

Thanks,
Abhi.

kduke · Post by **kduke** » Thu Aug 04, 2005 2:12 pm

The main function of hash files is for fast lookups.

ray.wurlod · Post by **ray.wurlod** » Thu Aug 04, 2005 4:32 pm

Very fast.

And it's hashed file, not hash file.

pnchowdary · Post by **pnchowdary** » Thu Aug 04, 2005 4:34 pm

They can also be used for eliminating duplicates.

ppalka · Post by **ppalka** » Fri Aug 05, 2005 1:30 am

And to handle multivalue fields

kumar_s · Post by **kumar_s** » Fri Aug 05, 2005 8:38 am

pnchowdary wrote:They can also be used for eliminating duplicates.

May i know how to eliminate duplicate using this stage, is it thru lookup with the same set of file or thru some other method.......

regards
kumar

ArndW · Post by **ArndW** » Fri Aug 05, 2005 8:42 am

Kumar,

the key in a hash file is always unique, so doing a subsequent WRITE to the same key will overwrite the previous value; thereby removing duplicates.

-Arnd.

kumar_s · Post by **kumar_s** » Fri Aug 05, 2005 8:48 am

ArndW wrote:Kumar,

the key in a hash file is always unique, so doing a subsequent WRITE to the same key will overwrite the previous value; thereby removing duplicates.

-Arnd.

Thanx Arnd i never thought about this...

regards
kumar

kollurianu · Post by **kollurianu** » Fri Aug 05, 2005 10:49 am

Code: Select all

And to handle multivalue fields

what does the above statement mean ppalka? can explain me...

Thanks a bunch,

ray.wurlod · Post by **ray.wurlod** » Fri Aug 05, 2005 7:15 pm

A multi-valued field (or column) may contain a list, rather than an atomic value. Some databases support the concept, though sometimes not using this terminology. This is particularly so with a database that promises OLAP capability (such as Oracle 9i/10g and MS SQL Server Plato) and databases with a Pick heritage (such as UniVerse, UniData, D3 and so on).
The main "support" for multi-valued data in DataStage is the ability automatically to "explode", or "un-nest", the multiple values to expose the "nested table" in at least first normal form.