On Sat, Nov 23, 2013 at 5:26 AM, Pepijn Van Eeckhoudt < [email protected]> wrote:
> Is datetime special in thuis context or will constant expression hoisting > like this happen for any function? > SQLite must know that the function always gives the same output given the same inputs. No every function works that way. Counterexamples include random() and last_insert_rowid(). But most built-in functions are factorable in the same way that datetime() is. Currently there is no API to designate an application-defined function as being "constant" in the sense that it always generates the same output given the same inputs. Hence, SQLite assumes the worst about application-defined functions and never tries to factor them out of the inner loop. Probably we should add a new API that allows the application to state auxiliary properties about application-defined functions (such as whether or not it is "constant", whether or not it can return NULL, whether or not it might change the encoding of its input parameters, etc.) But that has not been done yet. -- D. Richard Hipp [email protected] _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
