Rewrite a query that took 6-10 seconds into one that is near instantaneous.
Rewrite a query that took 6-10 seconds into one that is near instantaneous.

The old select that extracted external images visible to an experiment
had multiple left joins and examined 11M rows. The new query is a union
of two selects.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome