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Why does the join engine sometimes use indexes on join columns to match rows faster?

hard📝 Conceptual Q10 of 15
SQL - INNER JOIN
Why does the join engine sometimes use indexes on join columns to match rows faster?
AIndexes allow quick lookup of matching values, reducing search time
BIndexes store the join results permanently
CIndexes prevent duplicate rows in join results
DIndexes change the join condition automatically
Step-by-Step Solution
Solution:

  1. Step 1: Understand index purpose

    Indexes help find rows with specific values quickly without scanning entire table.

  2. Step 2: Apply to join matching

    The join engine uses indexes on join columns to speed up matching rows by fast lookups.

  3. Final Answer:

    Indexes allow quick lookup of matching values, reducing search time -> Option A

  4. Quick Check:

    Indexes speed up join matching by fast lookups [OK]
Quick Trick: Indexes speed up joins by quick value lookup [OK]
Common Mistakes:
MISTAKES
  • Thinking indexes store join results
  • Believing indexes remove duplicates
  • Assuming indexes change join logic

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