Hi, there doesn't seem to be much documentation about how to use lag() in monetdb, and I'm running into a cryptic error. Here is a snippet of a table: sql>select time, tcp_seq from packet_1_s order by time limit 10; +--------------------------+------------+ | time | tcp_seq | +==========================+============+ | 1436723208.3099999 | 2056936800 | | 1436723208.3099999 | 2056936800 | | 1436723208.3099999 | 2056936800 | | 1436723208.3099999 | 2056936800 | | 1436723208.3099999 | 2056936848 | | 1436723208.3099999 | 2056936848 | | 1436723208.3099999 | 2056936848 | | 1436723208.3099999 | 2056936848 | | 1436723208.3099999 | 2056936896 | | 1436723208.3099999 | 2056936896 | +--------------------------+------------+ 10 tuples (9.701ms) sql>select time, tcp_seq, lag(tcp_seq, 1) over (order by time) from packet_1_s order by time limit 10; TypeException:user.s22_25[502]:'calc.lag_grp' undefined in: _1678:any := calc.lag_grp(_1672:oid, _1674:oid, _1676:dbl) program contains errors Any ideas what causes this error? Thanks, Lars