Sessionizing Web Log Data using MySQL (perhaps by simulating window functions)
You've provided your own answer - MySQL doesn't have window-functions (AKA analytic functions). My advice to you would be to switch to PostgreSQL for that reason alone. 

Also, PostgreSQL supports SET operators, CHECK constraints, GIS, calculated fields (although MariaDB does support these),  and CTEs (Common Table Expressions, AKA the WITH clause) - although see Justin Swanhart's answer here.