SQL question

I just received this question from one of our developers: (my questions will follow)

<begin quote>

SELECT nmm.DOWNTIME_HEADER.DTHDR_RUN_DTE FROM nmm.DOWNTIME_HEADER
GROUP BY nmm.DOWNTIME_HEADER.DTHDR_RUN_DTE ORDER BY nmm.DOWNTIME_HEADER.DTHDR_RUN_DTE DESC;

vs. this version

select distinct dthdr_run_dte
from nmm.downtime_header
order by 1

<end quote>

Now, my first question is, what WOULD be the theoretical performance difference between the two, given growth to "tens of thousands" of rows?

Second, my first impulse is to do an EXPLAIN and a TKPROF to see which is better, but the current data volumes are so low, I'm not sure these tools would yeild anything useful. Received on Fri Apr 05 2002 - 08:27:50 CST