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Which clause is essential to use with LAG to define the order of rows?

easy📝 Conceptual Q2 of 15
SQL - Advanced Window Functions
Which clause is essential to use with LAG to define the order of rows?
AGROUP BY
BORDER BY
CWHERE
DHAVING
Step-by-Step Solution
Solution:

  1. Step 1: Identify how LAG determines previous rows

    LAG needs a defined order to know which row is previous, so it requires an ORDER BY clause.

  2. Step 2: Differentiate from other clauses

    GROUP BY groups rows, WHERE filters rows, and HAVING filters groups, none define row order.

  3. Final Answer:

    ORDER BY -> Option B

  4. Quick Check:

    LAG requires ORDER BY to define row sequence [OK]
Quick Trick: LAG needs ORDER BY to know previous row order [OK]
Common Mistakes:
  • Using GROUP BY instead of ORDER BY with LAG
  • Omitting ORDER BY causing unpredictable results
  • Confusing WHERE with ORDER BY

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