Set Operations

• Intersection and cross-product special cases of join.

• Union (Distinct) and Except similar; we’ll do union.

• Sorting based approach to union:

  • Sort both relations (on combination of all attributes).
  • Scan sorted relations and merge them.

• Hash-based approach to union:

  • Partition R and S using hash function h.
  • For each S-partition, build in-memory hash table (using h2), scan corresponding R-partition and add tuples to table while discarding duplicates.

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