Here’s an oddity that appeared on the OTN database forum last night:
We have this query in our application which works fine in 9i but fails in 11gR2 (on Exadata) giving an “ORA-00937: not a single-group group function” error….
… The subquery is selecting a column and it doesn’t have a group by clause at all. I am not sure how is this even working in 9i. I always thought that on a simple query using an aggregate function (without any analytic functions / clause), we cannot select a column without having that column in the group by clause. So, how 11g behaves was not a surprise but surprised to see how 9i behaves. Can someone explain this behaviour?
Yes, you heard that right- DBA Goth Cowgirl is getting an upgrade to Enterprise Manager, (EM12c) Goth Cowgirl! I will be starting as Oracle’s Consulting Member of the Technical Staff for the Strategic Customers Program, specializing in Enterprise Manager on March 17th.
Here are the slides of some of my previous presentations (that I haven’t made public yet, other than delivering these at conferences and training sessions):
Scripts and Tools That Make Your Life Easier and Help to Troubleshoot Better:
Troubleshooting Complex Performance Issues – Part1:
On Exadata (or when setting cell_offload_plan_display = always on non-Exadata) you may see the storage() predicate in addition to the usual access() and filter() predicates in an execution plan:
SQL> SELECT * FROM dual WHERE dummy = 'X'; D - X
Check the plan:
Another day, another airport lounge – another quick note: one of the changes that appeared in 12c was a tweak to the “broadcast” distribution option of parallel queries. I mentioned this in a footnote to a longer article a couple of months ago; this note simply expands on that brief comment with an example. We’ll start with a simple two-table hash join – which I’ll first construct and demonstrate in 184.108.40.206:
The OTN Yathra 2014 tour is over and I’m back home now. Here are all the blog posts from the tour.
Aanstaande dinsdag 4 maart wordt er door Oracle een Oracle EMEA Virtual Developer Day georganiseerd. Je kunt je hiervoor gratis inschrijven en live, via het internet, deze volgen, mocht je in de gelegenheid zijn. Je hebt de mogelijkheid om zelf mee te doen, via twee beschikbaar gestelde VirtualBox virtuele demo machine omgevingen, of alleen de
Sitting in an airport, waiting for a plane, I decided to read a note (pdf) about Flashback data archive written by Beat Ramseier from Trivadis. I’d got about three quarters of the way through it when I paused for thought and figured out that on the typical database implementation something nasty is going to happen after approximately 3 years and 9 months. Can you guess why ?
In the past I have enthused mightily about the benefits of the approximate NDV mechanism and the benefit of using auto_sample_size to collect statistics in 11g; however, as so often happens with Oracle features, there’s a down-side or boundary condition, or edge case. I’ve already picked this up once as an addendum to an earlier blog note on virtual stats, which linked to an article on OTN describing how the time taken to collect stats on a table increased dramatically after the addition of an index – where the index had this definition: