Sorry, duplicate postings from malfunctioning browser user:
When you MERGE datasets, they are typically assumed to be sorted by the merge key(s). This common usage of merge reads each dataset sequentially, which offers a lot of speed advantages. This is why @SASKiwi told you to sort the relevant files prior to the merge step.
True, merge can also work with unsorted data, but only if the merged datasets are indexed by the single merge key (or has a compound index on the multiple merge keys).
Avoiding pre-sorting is often why many programmers use PROC SQL to join files, but this approach does not have access to some of the tools available in merge (like the first. and last. dummy variables, or lag functions.
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