Implementing Projection

• Two parts:

(1) remove unwanted attributes,

(2) remove duplicates from the result.

• Refinements to duplicate removal:

  • If an index on a relation contains all wanted attributes, then we can do an index-only scan.
  • If the index contains a subset of the wanted attributes, you can remove duplicates locally.

SELECT DISTINCT

R.name,

R.phone

FROM Person R

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