Slightly over-aggressive join promotion in SQL for ordering
|Reported by:||Malcolm Tredinnick||Owned by:||Malcolm Tredinnick|
|Component:||Database layer (models, ORM)||Version:||master|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
Right now, we promote any table join used in the ordering portion to an outer join if it potentially contains NULL values (the corresponding Django field has
null=True). There are some cases where this is unnecessary. If we already used that join in the filter statements and didn't make it an outer join at that point, it's because we are already filtering out the null values, so an inner join still won't lose any results in the ordering.
Thus, we should only promote joins for ordering if we needed to add that join for the ordering (this means
self.alias_refcount[...] == 1, or something else that's easily detectable).
Noting this so I don't forget. Don't want to introduce new bugs at the moment and it's a bit of an edge case, so it can wait until post-1.0.