On Fri, Oct 19, 2012 at 5:08 AM, Steinar Midtskogen <stei...@latinitas.org>wrote:
> Hi > > Suppose I have a virtual table v with a column c. Then, if I do: > > SELECT c, c+1, c-1 FROM v; > > xColumn() will then only be called once per row. Which is all good. > > But if I add any constraints on c, e.g.: > > SELECT c, c+1, c-1 FROM v WHERE c IS NOT NULL; > > Then xColumn() will get called a second time for c, which seems > wasteful if c takes time to compute. Or very bad if the computation > has side effects (which it probably shouldn't have). > > Is there any reason for this behaviour? > xColumn() might be called any number of times for a single column - once, one hundred times, not at all. SQLite makes no guarantees about this. The virtual table implementation must return the same value for all calls. The reason is that it is sometimes convenient for the SQLite core to call xColumn multiple times and that it is not normally a problem for the virtual table to implement this efficiently, using caching if necessary. > > My SQlite version is 3.7.14. > > -- > Steinar Midtskogen > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
