There are some important differences between sequences defined by &NDBSEQ, and sequences built by &NDBSCAN:
&NDBSCAN-built sequences are represented as an in-storage list of RIDs (the actual order depending on SORT, and so on). If the list is ordered on RID, the previous example repositions from 10 to 15, and back to 10, as SKIP=n instructs &NDBGET to skip over n-1 entries in the list. Only when the target RID has been deleted, does &NDBGET proceed to the next RID in the list, until a non-deleted record is found.
&NDBSCAN-built sequences take storage proportional to the number of matching records to hold the list. Thus, you should try to minimize the number of concurrent scan sequences in use, particularly if using &NDBSCAN in an EASINET procedure.
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