TESTS TO ADD * Test that ":db-kind :key" adds an index for that key. This is complicated by different backends showing autogenerated primary key in different ways. * :db-constraint tests * Number and Char field types * symbol slot * generalized-boolean slot OPTIMIZATIONS * Revisit result-type list creation, perhaps caching * Rework LIST-ATTRIBUTE-TYPES and LIST-INDEXES such that they exhibit their current behaviours using single database queries. * Possible use of cached attribute type information for operations which insert/update records as mentioned in the CommonSQL user guide. * Extend caching of generated SQL strings to more complex expressions which are likely to be repeatedly executed many times. POSSIBLE EXTENSIONS * improve large object api and extend to databases beyond postgresql * add support for prepared statements