Suppose TblB has primary key ColB and contains a column ColBX TblC has primary key ColC and contains a column ColCX TblD has primary key ColD and contains a column ColDX
TblA has primary key ColA and also contains columns ColB, ColC and ColD (i.e. TblB, TblC and TblD are effectively lookup tables for TblA). If I run the following query explain select ColA from TblA left join TblB using (ColB) left join TblC using (ColC) left join TblD using (ColD) where ColBX=?; there will be no trace of TblC or TblD as they're redundant. If i run the following query explain select ColA from TblA left join TblB using (ColB) left join TblC using (ColC) left join TblD using (ColD) where ColCX=?; there will be no trace of TblD as it's redundant but what I need explaining is why is TblB included in the explain. I'm guessing that the sqlite query optimiser finds it easy to ignore trailing redundant tables but checking for other redundant tables is too expensive. Is that the case or am I missing something and the inclusion of TblB is necessary to get the correct result? _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
