This page is a quick reference checkpoint for LAG in IBM DB2: 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.
Returns the value from the row offset positions before the current row within the partition; returns NULL or default-value when offset goes out of range; IGNORE NULLS skips rows where the expression is NULL.
If this behavior feels unintuitive, the tutorial below explains the underlying pattern step-by-step.
Supports LAG(expr, offset, default); offset must be a positive integer and defaults to 1; optional default-value and IGNORE NULLS clause.
SELECT LAG(salary) OVER (PARTITION BY dept ORDER BY empno) FROM employee;
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 IBM DB2 Documentation →Looking for more functions across all SQL dialects? Visit the full SQL Dialects & Window Functions Documentation.