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You wrote:

medium📝 Debug Q6 of 15
PostgreSQL - Joins in PostgreSQL
You wrote:
SELECT * FROM orders NATURAL JOIN customers;
But the query returns unexpected results. What is a likely cause?
AYou forgot to add an ON clause.
BThe tables have multiple columns with the same name, causing unintended join keys.
CNATURAL JOIN does not work with SELECT *.
DThe tables have no columns with the same name.
Step-by-Step Solution
Solution:
  1. Step 1: Understand NATURAL JOIN behavior

    NATURAL JOIN uses all columns with the same name as join keys automatically.
  2. Step 2: Identify cause of unexpected results

    If multiple columns share the same name, the join condition may include unintended columns, causing unexpected output.
  3. Final Answer:

    The tables have multiple columns with the same name, causing unintended join keys. -> Option B
  4. Quick Check:

    Unexpected results = multiple same-named columns [OK]
Quick Trick: Multiple same-named columns cause unexpected NATURAL JOIN keys [OK]
Common Mistakes:
  • Thinking NATURAL JOIN needs ON clause
  • Believing SELECT * affects NATURAL JOIN behavior
  • Assuming no same-named columns means no join

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