Oracle

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SQL for Beginners : Videos and Articles

love-sqlI’ve been saying for some time I should do some more entry level content, but it’s been kind-of hard to motivate myself. I mostly write about things I’m learning or actively using, so going back and writing entry level content is not something that usually springs to mind.

Recently I’ve got involved in a number of “grumpy old man” conversations about the lack of SQL knowledge out there. That, combined with a few people at work getting re-skilled, prompted me to get off my ass and give it a go. It’s actually quite difficult trying to get yourself into the head-space of someone who is coming fresh to the subject. You don’t want to pitch it too low and sound patronizing, but then pitching it too high makes you sounds like an elitist dick.

Jonathan Lewis's picture

Histogram Tip

I’ve just responded to the call for items for the “IOUG Quick Tips” booklet for 2015 – so it’s probably about time to post the quick tip that I put into the 2014 issue. It’s probably nothing new to most readers of the blog, but sometimes an old thing presented in a new way offers fresh insights or better comprehension.

Histogram Tips

A histogram, created in the right way, at the right time, and supported by the correct client-side code, can be a huge benefit to the optimizer; but if you don’t create and use them wisely they can easily become a source of inconsistent performance, and the automatic statistics gathering can introduce an undesirable overhead during the overnight batch. This note explains how you can create histograms very cheaply on the few columns where they are most likely to have a beneficial effect.

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Oracle Midlands : Event #11 – Summary

oracle-midlandsLast night was Oracle Midlands event #11 with Chris Antognini.

The lead up to this event was not the best for me. I had been on the verge of a headache all day. By 14:00 I gave up, went home and went to sleep for a couple of hours. It wasn’t great, but it was just enough to take the edge off, so when the time came, I felt sort-of OK to head out for the event. The drive started to convince me this wasn’t the best move, but once I got to the event and sat down I figured I was going to make it. :)

Chris did two talks at the event.

Jonathan Lewis's picture

IN/EXISTS bugs

Here’s a simple data set – I’m only interested in three of the columns in the work that follows, but it’s a data set that I use for a number of different models:

Jonathan Lewis's picture

Index Usage – 4

Here’s a thought that came to me while I was writing up a note about identifying redundant indexes a few minutes ago. Sometimes you end up supporting applications with unexpected duplication of data and indexes and need to find ways to reduce overheads. Here’s some code modelling a scenario that I’ve seen more often than I like (actually, just once would be more often than I’d like):

Jonathan Lewis's picture

Index Usage – 3

In my last note on index usage I introduced the idea of looking at v$segstat (or v$segment_statistics) and comparing the “logical reads” statistic with the “db block changes” statistic as an indicator of whether or not the index was used in execution plans. This week I’ll explain the idea and show you some results – with a little commentary – from a production system that was reported on the OTN database forum.

dbakevlar's picture

Raspberry Pi Controlled Airplane Launcher

Everything I do with the Raspberry Pi is about finding ways to incorporate STEAM, (Science, Technology, Engineering, Art and Math) into my projects.  This is no easy feat, but I have a lot of fun while I try.  This latest project, we’re still working on ways to “enhance” and understand how code can be used with multiple projects and to satisfy multiple requirements.

Jonathan Lewis's picture

Index Usage – 2

I’ve been a little slow in the follow-up to my previous posting on possibly redundant indexes. Before going into the slightly more complex stuff, there’s another peripheral point (but a very important one) that’s worth raising about how clever the optimizer can be. Here’s some code for 11.2.0.4 to demonstrate the point:

dbakevlar's picture

Creating a Trace File from EM12

Creating a trace file from EM12c is quite easy and doesn’t require a DBA offering up the world to allow a developer or support person to perform this action.

oraclebase's picture

Oracle Cloud : First Impressions

cloudFollowers of the blog will know I’ve been waiting to get access to the Oracle Cloud for a while. Well, I’ve finally got access to a bit of it. Specifically, the “Oracle Database Cloud Service” (DBaaS) part. :)

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