This page is a quick reference checkpoint for LAG in MariaDB: 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 from a previous row determined by the ORDER BY clause; default offset = 1
If this behavior feels unintuitive, the tutorial below explains the underlying pattern step-by-step.
LAG(expr[ , offset]) OVER ( [ PARTITION BY partition_expression ] ORDER BY order_list )
SELECT department, employee, LAG(salary) OVER (PARTITION BY department ORDER BY salary) AS previous_salary FROM employees;
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 MariaDB Documentation →Looking for more functions across all SQL dialects? Visit the full SQL Dialects & Window Functions Documentation.