Window Functions (79–88)
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What is a window function?
It performs calculations across rows without collapsing them.
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What is ROW_NUMBER()?
Assigns unique row number.
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What is RANK()?
Assigns rank with gaps for ties.
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What is DENSE_RANK()?
Assigns rank without gaps.
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Difference between RANK and DENSE_RANK?
RANK skips numbers after tie; DENSE_RANK does not.
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What is PARTITION BY?
Divides result set into groups for window functions.
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Find highest salary in each department.
Use RANK() with PARTITION BY dept.
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What is LEAD()?
Fetches next row value.
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What is LAG()?
Fetches previous row value.
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Scenario: Compare current month sales with previous month.
Use LAG(sales).
