LAG() window function for period-over-period comparison
Board trend slide. For each revenue account, show year, total revenue, prior-year revenue (LAG), and YoY % change. Columns: `account_name`, `year`, `revenue`, `prior_revenue`, `yoy_pct`. Posted only.
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First aggregate revenue by (account_name, year) in a subquery.
Then apply `LAG(revenue) OVER (PARTITION BY account_name ORDER BY year) AS prior_revenue`.
`yoy_pct = (revenue - prior_revenue) / NULLIF(prior_revenue, 0)`. The earliest year per account will have NULL — that's expected.