A database system includes an enhanced technique for performing sorts in which removals of duplicate records are performed to compact the size of segments being sorted. To enhance a query plan, the duplicate record removal is performed as early in the query plan as possible. By removing duplicate records early in the query plan, the number of input/output (I/O) operations is reduced, resulting in more efficient usage of database system resources. In example implementations, two type of sorts are performed: a heap sort (to sort successive segments of an input file, with the sorting associated with concurrent removal of duplicate records to compact each segment so that a smaller number of I/O accesses is needed); and a merge sort (in which output files from prior sorting passes are merged and sorted, with the merge sort process also associated with the removal of duplicate records to further compact the data segments and reduce the number of I/O accesses).

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