SQL-question (two fields in one)

I have a problem where I need to check if I have duplicates of my data. The data is stored in a table, where the combination of two fields together make the rows unique. This makes checking for duplicates difficult, (or at least I have not found a solution). What I need to do (I think) is some way to select the two important fields "together" into one field in a temporary table, so that they make out one unique string. Does anybody know how to do this in sqlplus, or do I need more sophisticated tools to do it? (for the moment, sqlplus is all I have) And last but not least; HOW do I do it?

(I was thinking of unloading the data to a text-file, and using the unix-command "sed" to paste the two fields together, but this seems like a problem "somebody must have had before", so I hope you guys can give me a better suggestion...)

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Roar Pettersen
roar_at_link.no
http://www.link.no/roar/