After sorting data is missing

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Hi, I'm running into a problem I've never seen before. I'm trying to sort a character variable that has a unique identifier, after the data is sorted, the data within the variable goes missing. Any insight as to why?

proc sort data=work.data; by uniqueID_char; run;

I've verified that the data exists before the proc sort command, so I'm not sure why its deleting it.

[Reeza · Accepted solution]

Post the log please. Run a proc freq on you data before and after the sort and compare the results. 

You probably have some missing data and the sort brings it to the top of the dataset since missing is the smallest value. 

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Thanks for the suggestion. My data set is 110M, I didn't think it was possible for it to be missing 800K, but it appears it is.