Create a copy of a table while ommitting and concatenating columns

I have two tables. The first table is OEPCPHCSP. This table has lots of columns(at least 100 or so). The second table is OEPCPHOCAS. I want this table to be an exact copy of the first table(OEPCPHCSP) - with a few exceptions. My first table(OEPCPHCSP) has these four fields: oecc01, oeyr01, oemo01, and oedy01. These fields should not be included in the second table(OEPCPHOCAS). Instead I would like to concatenate those four fields from the first table(OEPCPHCSP) into one field call INVDAT in the second table(OEPCPHOCAS). I have tried using concat, but did not get very far with that. I'm pretty lost right now as to how to do this. And it doesn't seem like I can copy the table over due to different column numbers. Any help is appreciated.