Hello, Haikuo, Taking the last comment first, yes, a Proc SQL with 'Left Outer Join' works perfectly. The problem gets to be the time to do it. I have been testing out Hashing and it runs in half the CPU time and only 20% of the elapsed time of the Proc SQL. I am fairly new to Hashing in SAS and I will look into Hiter. I have not seen anything (yet!) in the documentation to find which of the items in the Hash table have NOT been matched with an item in the Many table. (This is definitely only a One-to-Many, with the Many possibly being Zero.) I understand the process of having two hash tables and, for the second one, keeping only the non-matched items, but that hash table has the potential to be HUGE compared the One table. The vast majority of items in the Many table will not match an item in the One table as the One table has been restricted in scope depending on the query. Again, I have not gone through all of the documentation out there. So, is there a way, using hiter, to set an indicator in the hash table whenever there is a match? And then, query the hash table to find out what has NOT been matched? Kind Regards, Wayne
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