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Why does SQL require columns to have compatible data types and matching counts in set operations like UNION or INTERSECT?

hard📝 Conceptual Q10 of 15
SQL - Set Operations
Why does SQL require columns to have compatible data types and matching counts in set operations like UNION or INTERSECT?
ATo guarantee that column names are identical across queries.
BTo enforce that all tables have the same schema.
CTo allow ORDER BY clauses to work on all combined queries.
DTo ensure rows from different queries can be combined into a single result set correctly.
Step-by-Step Solution
Solution:

  1. Step 1: Understand set operation behavior

    Set operations combine rows vertically into one result set.

  2. Step 2: Explain why matching columns and types matter

    Compatible columns ensure data aligns correctly for each row in the combined output.

  3. Final Answer:

    To ensure rows from different queries can be combined into a single result set correctly. -> Option D

  4. Quick Check:

    Reason for column matching = C [OK]
Quick Trick: Compatible columns ensure correct combined results [OK]
Common Mistakes:
MISTAKES
  • Thinking schemas must be identical
  • Believing column names must match
  • Confusing with ORDER BY requirements

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