note: to debug the embedded server,
% cmake -DWITH_EMBEDDED_SERVER=ON -DCMAKE_BUILD_TYPE=Debug -DWITH_DEBUG=1 ..

note: when changing the mysql grammar, it's necessary to re-run cmake,
which runs the equivalent of lex and yacc on sql_yacc.yy.  It's easiest
to just "rm -r build; mkdir build; cd build; cmake ... etc".

Some notes about Item processing:
    Item::transform, Item::compile, and Item::traverse_cond could be useful