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SQL Window Functions: LAG, LEAD, Deltas, and Time-Series Comparisons/Provide a LAG default value

Avoid NULL on the first row.

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Section: LAG and LEAD basics

Provide a LAG default value

sql
sql
SELECT day,
       revenue,
       LAG(revenue, 1, 0) OVER (ORDER BY day) AS prev_revenue_or_zero
FROM daily_revenue;
Explanation

The third argument is the default when an offset row does not exist.

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