Paolo Bolzoni wrote: > sqlite> explain query plan SELECT id FROM tour LIMIT 1; > 0|0|0|SCAN TABLE tour USING COVERING INDEX tour_unsorted_path_idx > (~1000000 rows) > > I am not still sure I understand completely the output of explain > query plan.
It means that SQLite estimates that the table (or its index) contains about 1000000 rows. The LIMIT clause is *not* used for this estimate. > To get this simple result, sqlite3 actually scans the whole > table? No. Without the LIMIT, the query would scan the entire index. With the LIMIT, the scan is stopped after the first row. > I just have a question about query written in the begin, in my > application I use it to know if a table is empty. I execute it > and just use sqlite3_step return value. Errors a part, if it is > SQLITE_DONE the table is empty, if it is SQLITE_ROW it is not. This is more a documentation than an optimization improvement, but if you are not interested in the value of any particular column, you should not request it in the first place; i.e., use something like: SELECT 0 FROM tour LIMIT 1; Regards, Clemens _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
