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Consider tables:

medium📝 query result Q5 of 15
SQL - LEFT and RIGHT JOIN
Consider tables:

Authors:
ID | Name
1 | Alice
2 | Bob

Books:
ID | AuthorID | Title
10 | 1 | Book A
11 | 3 | Book B

What will this query return?
SELECT Authors.Name, Books.Title FROM Authors LEFT JOIN Books ON Authors.ID = Books.AuthorID;
AAlice Book A, Bob Book B
BAlice NULL, Bob NULL
CAlice Book B, Bob NULL
DAlice Book A, Bob NULL
Step-by-Step Solution
Solution:
  1. Step 1: Match Authors to Books

    Alice (ID 1) matches Book A; Bob (ID 2) has no matching book; Book B's AuthorID 3 does not match any author.
  2. Step 2: LEFT JOIN result

    All authors appear; unmatched Bob has NULL for book title.
  3. Final Answer:

    Alice Book A, Bob NULL -> Option D
  4. Quick Check:

    LEFT JOIN unmatched right rows = NULL [OK]
Quick Trick: LEFT JOIN keeps all left rows, unmatched right columns are NULL [OK]
Common Mistakes:
MISTAKES
  • Including unmatched right table rows
  • Assigning wrong book titles
  • Ignoring NULLs for unmatched rows

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