Hi Art, Thanks for your replies. I have about 10 years worth of data split up into monthly SAS data files. The files are labelled yyyymm and have about 1million IDs (rows) and about 125 variables (col) in each dataset. I would like to find out information on 80000 IDs which have an open date variable and is held in a SAS dataset. I want to pull the same variables for each ID from the monthly tables corresponding to the table which holds data 1 year on from the open date. The IDs have different open dates over the 10year period. The matching would be 1 to 1 on the IDs. I want a snapshot of how the ID is doing after 1 year. If I join all the monthly files together, won't this be quite inefficient? 10x12x1million or 10x12x80000 if I only keep those IDs I'm interested in. Many thanks, Bo
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