This page is a quick reference checkpoint for LAG in Snowflake: behavior, syntax rules, edge cases, and a minimal example; plus the official vendor documentation.
LAG lets you look back at a previous row's value within the same partition.
Accesses data in a previous row in the same partition; default offset is 1; default value is NULL; supports IGNORE NULLS and RESPECT NULLS.
If this behavior feels unintuitive, the tutorial below explains the underlying pattern step-by-step.
LAG ( <expr> [ , <offset> , <default> ] ) [ { IGNORE | RESPECT } NULLS ] OVER ( [ PARTITION BY <expr1> ] ORDER BY <expr2> [ { ASC | DESC } ] )
SELECT emp_id, year, revenue, LAG(revenue, 1, 0) OVER (PARTITION BY emp_id ORDER BY year) AS diff_to_prev FROM sales;
If you came here to confirm syntax, you’re done. If you came here to get better at window functions, choose your next step.
LAG is part of a bigger window-function pattern. If you want the “why”, start here: Lead Lag
Reading docs is useful. Writing the query correctly under pressure is the skill.
For the authoritative spec, use the vendor docs. This page is the fast “sanity check”.
View Snowflake Documentation →Looking for more functions across all SQL dialects? Visit the full SQL Dialects & Window Functions Documentation.