Join - dealing with different input column names

juliank · Post by **juliank** » Fri Apr 11, 2008 9:20 am

What are the best practices for dealing with joins where the incoming column names don't match? Is there more than one approach? I thought that renaming column(s) under the input tab for a join will work, but it doesn't. If this is the case, which stage(s) are best suited to do this?

Thanks for any input!

kumar_s · Post by **kumar_s** » Fri Apr 11, 2008 9:26 am

Renaming the column in prior stages where its permisible to rename like, Transformer, modify etc,.
Or Lookup and do a lookup with different column names.

juliank · Post by **juliank** » Fri Apr 11, 2008 9:34 am

Thanks!

Do you maybe know what is the point of allowing to rename column names in a join (Input -> Columns), but not being able to take advantage of it? Maybe I am missing something.

Also, is there a performance penalty for using one or the other stage for something simple like renaming columns?

kumar_s · Post by **kumar_s** » Fri Apr 11, 2008 12:56 pm

It is not stage but in the link that connects Join and the prior stage. If you rename the column in Join input stage, output stage of the previous gets changed, and hence the actual rename is happening in the previous stage.
More the stage, more the resource been consumed. There are few stages with less/No resource consumption like Copy stage etc.,

juliank · Post by **juliank** » Fri Apr 11, 2008 1:18 pm

kumar_s wrote: ... If you rename the column in Join input stage, output stage of the previous gets changed, and hence the actual rename is happening in the previous stage.

Agree. So if a rename was made, and I see it, why wouldn't it be enough to accomplish now a join on columns that have identical names on the input stage of the join? I am just trying to understand. Maybe I am missing something.

kumar_s · Post by **kumar_s** » Fri Apr 11, 2008 1:21 pm

Are you getting any error or warning? What is the stage prior to the Join stage?

juliank · Post by **juliank** » Fri Apr 11, 2008 1:33 pm

kumar_s wrote:Are you getting any error or warning? What is the stage prior to the Join stage?

I don't get any error during the design stage. When I pull down the menu for keys to join, the list is blank even that I changed the input names to match where required. I don't know whether this a bug, or something that I just need to learn.

In this case there are three inputs into this join. The sources for these inputs are two joins and one dynamic rdbms source (table).

kumar_s · Post by **kumar_s** » Fri Apr 11, 2008 1:42 pm

It should show up the column names if they match in the pull down box for key list. Check carefully for spelling in each link. If you are using the same metadata, try to save one and reload into other link.

ray.wurlod · Post by **ray.wurlod** » Fri Apr 11, 2008 4:44 pm

Copy is the cheapest stage for renaming columns.

John Smith · Post by **John Smith** » Mon Apr 14, 2008 7:53 pm

juliank wrote:
kumar_s wrote: ... If you rename the column in Join input stage, output stage of the previous gets changed, and hence the actual rename is happening in the previous stage.
Agree. So if a rename was made, and I see it, why wouldn't it be enough to accomplish now a join on columns that have identical names on the input stage of the join? I am just trying to understand. Maybe I am missing something.

Yes but are those columns defined as Keys ?