Calculate Month-over-Month Growth with LAG() in SQL

Question

Given monthly revenue records, compute the month-over-month revenue percentage change: `((current - previous) / previous) * 100`, rounded to 2 decimal places.

Accepted Answer

Optimal Solution:
WITH revenue_lag AS (
  SELECT 
    revenue_month,
    revenue,
    LAG(revenue, 1) OVER (ORDER BY revenue_month ASC) AS prev_revenue
  FROM monthly_revenue
)
SELECT 
  revenue_month,
  revenue,
  prev_revenue,
  ROUND(
    100.0 * (revenue - prev_revenue) / prev_revenue, 
    2
  ) AS mom_growth_pct
FROM revenue_lag
ORDER BY revenue_month ASC;

Technical Explanation:
`LAG(revenue, 1) OVER (ORDER BY revenue_month ASC)` retrieves the previous row's revenue. The outer query computes the growth percentage.

revenue_month	revenue
2026-01	100000
2026-02	125000
2026-03	118750

revenue_month	revenue	prev_revenue	mom_growth_pct
2026-01	100000	NULL	NULL
2026-02	125000	100000	25
2026-03	118750	125000	-5