From Michelle Gower at https://lsstc.slack.com/archives/C2JPT1KB7/p1553801514017200:

For each run there were a bunch of
```DELETE FROM "PatchSkyPixJoin" WHERE "PatchSkyPixJoin".tract = :tract_1 AND "PatchSkyPixJoin".skymap = :skymap_1 AND "PatchSkyPixJoin".patch = :patch_1```
statements which at first glance seem to be coming from the pipeline. If they are from the pipeline (instead of the gen3.py or other bootstrap codes), then we should talk sometime about why there is a delete.

These tables should be inserted into in gen2convert, but not deleted from.  They should not be modified at all during processing.  It's possible I'm just clearing subset of a table before inserting into it, which would mean in this case these DELETEs are no-ops because there are no matching record.  If that's the case, we might be able to ignore this.