You have two tables with duplicate keys: Table A: (id, val) Table B: (id, val) When joining on id, how does the join engine handle multiple matching rows?
AIt picks only the first matching row from Table B
BIt creates a row for every combination of matching rows (Cartesian product for matches)
CIt returns an error due to duplicate keys
DIt ignores duplicates and returns only unique rows
Step-by-Step Solution
Solution:
Step 1: Understand join with duplicates
When multiple rows match on join keys, the engine pairs each matching row from both tables.
Step 2: Resulting row count
This creates a Cartesian product of matching rows for those keys.
Final Answer:
It creates a row for every combination of matching rows (Cartesian product for matches) -> Option B
Quick Check:
Join duplicates produce all matching pairs [OK]
Quick Trick:Joins multiply rows when keys have duplicates [OK]
Common Mistakes:
MISTAKES
Thinking join picks only one match
Assuming duplicates cause errors
Believing duplicates are automatically removed
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