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August 2013

Scalar Subqueries in Oracle SQL WHERE clauses (and a little bit of Exadata stuff too)

My previous post was about Oracle 12c SQL Scalar Subquery transformations. Actually I need to clarify its scope a bit: the previous post was about scalar subqueries inside a SELECT projection list only (meaning that for populating a field in the query resultset, a subquery gets executed once for each row returned back to the caller, instead of returning a “real” column value passed up from a child rowsource).

I did not cover an other use case in my previous post – it is possible to use scalar subqueries also in the WHERE clause, for filtering the resultset, so let’s see what happens in this case too!

Scalar Subqueries in Oracle SQL WHERE clauses (and a little bit of Exadata stuff too)

My previous post was about Oracle 12c SQL Scalar Subquery transformations. Actually I need to clarify its scope a bit: the previous post was about scalar subqueries inside a SELECT projection list only (meaning that for populating a field in the query resultset, a subquery gets executed once for each row returned back to the caller, instead of returning a “real” column value passed up from a child rowsource).

I did not cover an other use case in my previous post – it is possible to use scalar subqueries also in the WHERE clause, for filtering the resultset, so let’s see what happens in this case too!

SQL joins visualized in a surprising way

Saw a good posting on SQL joins today that echoes a classic image of SQL joins:

Visual_SQL_JOINS_orig

I loved this graphic when I first saw it. Seeing the graphic made me think “wow, I can actually wrap my mind around these crazy SQL joins.”

But there is more to SQL joins than meets the eye, at least in these pictures. These pictures leave out the effects of projection and amplification. For example, just taking the simplest case of a two table join (an inner join):

Creating a 12c Container Database from scripts

If you are curious how to create a CDB without the help of dbca then the “generate scripts” option is exactly the right approach! I am a great fan of creating databases with the required options only-the default template (General Purpose) is dangerous as it creates a database with options you may not be licensed for and additionally opens security risk.

The best^H^H^Heasiest way to understand how a Container Database (CDB from now on) is created is to let dbca create the scripts. The process is the same as with an interactive installation except that at the very end you do NOT create the database but tick the box to generate the scripts.

The resulting scripts will be created in $ORACLE_BASE/admin/${ORACLE_SID}/scripts. Change directory to this location and you will be surprised about the sheer number of files ending in *.sql

Facebook Schema and Peformance

From the article “Facebook shares some secrets on making MySql scale

“800 million users and handling more than 60 million queries per second” …”4 million row changes per second.”

and that was almost a two years ago. Think what it’s like now!

Ever wonder why Facebook limits your friends to 5000?  Does Facebook want to stop people from using it to promote themselves?

Ever see this message “There are no more posts to show right now” on Facebook?

Notice it says “There are no more posts to show right now.”

Delphix finalist for UKOUG partners of the year

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Delphix  is a finalist for UKOUG partners of the year!

See the finalist at UKOUG finalists for partner of the year

Vote here : UKOUG parnter of the year awards 2013

Also on the list are fellow Oaktable related organizations Scalabilities and Enkitec


Delphix


 

Kyle Hailey

Enkitec is a finalist for the UKOUG Engineered Systems Partner of the Year Award

Enkitec has made it to the shortlist of UKOUG Partner of the Year Awards, in the Engineered Systems category. So if you like what we have done in the Exadata and Engineered Systems space, please cast your vote! :-)

Note that you need to be an Oracle user – using your company email address in order to vote. (the rules are explained here).

Thanks!!!

Latency heatmaps in D3 and Highcharts

See Brendan Gregg’s blog on how important and cool heatmaps can be for showing latency information and how average latency hides what is really going on:

Now if we want to create heatmap graphics, how can we do it? Two popular web methods for displaying graphics are Highcharts and D3. Two colleges of mine whipped up some quick examples in both Highcharts and D3 to show latency heatmaps and those two examples are shown below. The data in the charts is random just for the purposes of showing examples of these graphics in actions.

We are proud to be finalists AGAIN for UKOUG Database Partner of the Year!

We are very proud to once again be shortlisted as the UKOUG Database Partner of the Year! We would love to make it two years in a row, so if you think we do a great job we'd love to receive your support. The alphabetical shortlist is available here for all categories. To vote, you simply […]