Prevent calculation from being done 3 times

H2 calls this function 3 times, sometimes just to get the column names.
This is a hack to prevent the calculation from being done 3 times. It is
done only when necessary. See
    https://groups.google.com/forum/#!topic/h2-database/NHH0rDeU258
Merge pull request #228 from agouge/perf

Prevent calculation from being done 3 times
H2 calls this function 3 times, sometimes just to get the column names.
This is a hack to prevent the calculation from being done 3 times. It is
done only when necessary. See
https://groups.google.com/forum/#!topic/h2-database/NHH0rDeU258