[Solved] Why does the INTERSECT operator remove duplicates in PostgreSQL result sets? — Ans: Because INTERSECT returns a set, which by definition has unique elements | PostgreSQL

PostgreSQL - Set Operations and Advanced Queries

Why does the INTERSECT operator remove duplicates in PostgreSQL result sets?

ABecause duplicates cause syntax errors with INTERSECT

BBecause INTERSECT returns a set, which by definition has unique elements

CBecause INTERSECT uses DISTINCT internally by default

DBecause INTERSECT only works on primary keys

Step-by-Step Solution

Solution:

Step 1: Understand set operations in SQL
INTERSECT returns the intersection of two sets, and sets contain unique elements only.
Step 2: Recognize that duplicates are removed by definition
Therefore, duplicates are removed automatically to maintain set semantics.
Final Answer:
Because INTERSECT returns a set, which by definition has unique elements -> Option B
Quick Check:
INTERSECT returns unique rows by set definition [OK]

Quick Trick: INTERSECT results are unique because sets have no duplicates [OK]

Common Mistakes:

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Why does the INTERSECT operator remove duplicates in PostgreSQL result sets?