factored "sequence" execution in postgres in oracle to be generalized to the SQLEngin...

factored "sequence" execution in postgres in oracle to be generalized to the SQLEngine, to also allow space for "defaults" that may be constants, python functions, or SQL functions/statements
Sequence schema object extends from a more generic "Default" object
ANSICompiled can convert positinal params back to a dictionary, but the whole issue of parameters and how the engine executes compiled objects with parameters should be revisited
mysql has fixes for its "rowid_column" being hidden else it screws up some query construction, also will not use AUTOINCREMENT unless the column is Integer