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What does a LEFT JOIN do in SQL?

easy📝 Conceptual Q11 of 15
SQL - LEFT and RIGHT JOIN
What does a LEFT JOIN do in SQL?
AReturns all rows from the left table and matched rows from the right table, NULL if no match.
BReturns only rows that have matching values in both tables.
CReturns all rows from the right table and matched rows from the left table.
DDeletes rows from the left table that have no match in the right table.
Step-by-Step Solution
Solution:

  1. Step 1: Understand LEFT JOIN behavior

    A LEFT JOIN keeps all rows from the left table regardless of matches in the right table.

  2. Step 2: Identify NULLs for unmatched rows

    If there is no matching row in the right table, the result shows NULL for right table columns.

  3. Final Answer:

    Returns all rows from the left table and matched rows from the right table, NULL if no match. -> Option A

  4. Quick Check:

    LEFT JOIN = all left rows + NULL for no match [OK]
Quick Trick: LEFT JOIN keeps all left rows, unmatched right rows show NULL [OK]
Common Mistakes:
MISTAKES
  • Confusing LEFT JOIN with INNER JOIN
  • Thinking unmatched rows are dropped
  • Assuming NULLs appear in left table columns

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