Currently, there is no way of obtaining the last insert id using the Ruby Driver.
The reason why this is a major bug is because it affects one of our affiliates and I quote here:
"OK. When I finished up my work yesterday, I had most things working
using CUBRID's jdbc driver on JRuby. I'm going to work on supporting
the cubrid ruby gem on regular ruby later today. However, if it can't
return the last inserted ID, a good portion of Sequel's test suite will
The reason why this a bug also and not just a feature request is because the last insert id cannot be obtained neither by executing the query "SELECT LAST_INSERT_ID()" from the ruby driver and then getting the result (which is "nil").