Scheduler Optimization

[Rob Smith]

SELECT DISTINCT is pretty inefficient compared to GROUP BY, so this patch switches a DISTINCT for a GROUP BY and should be functionally equivalent. Wanted to run it by you before committing.

[gigem]

I believe this patch has a very high degree of causing subtle breakage in the scheduler. The scheduler has used SELECT DISTINCT since before I started mucking with it and is full of assumptions that every returned row is unique. The only way to safely switch to GROUP BY is to thoroughly check the usage of every column returned in the query. At a minimum, recordid, manualid and probably oldrecduplicate, recduplicate and findduplicate would need to be included in any GROUP BY clause.

[gigem]

After rechecking the BUQ, I think the GROUP BY fields would need to be recordid, chanid, starttime, manualid and cardinputid. However, I'm now pretty sure that previous tweaking of the BUQ made the DISTINCT (and GROUP BY) superfluous. IOW, I think the DISTINCT can simply be removed.

Good catch, kormoc, although, the speedup I see is negligible at best.

[gigem]

(In [25836]) Removed "DISTINC" from the BUQ in the scheduler. It was made superfluous by previous restructuring of the query. Based on a patch from kormoc. Fixes #8819.