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SQL

On the Topic of Programming 3

September 3, 2012 (Back to the Previous Post in the Series) In the previous article in this series, a question was posed regarding how many SQL statements would be required to generate the following report, which displays in Microsoft Excel: A significant number of items regarding the report require explanation: Employee IDs and employee names [...]

On the Topic of Programming 2

September 2, 2012 (Back to the Previous Post in the Series) (Forward to the Next Post in the Series) Over the course of the last six months I developed several efficiency reports for the machining facility where I work, measuring the average time required to complete a customer’s part compared to the engineering standard “target” run [...]

On the Topic of Programming 1

August 26, 2012 (Forward to the Next Post in the Series) As those of you who have read this blog’s About page probably know, my day to day job responsibilities involve a lot of activities that are not specific to Oracle Database performance tuning, or even remotely Oracle DBA type activities.  Those extra acttivites are part of what [...]

Exclusion of Unioned SQL in Views – Followup

Last week I put up a post about how Oracle can filter out sections of a union view..

Within the comments I put up another example where the CBO did not filter out all but one of the Union views despite my replicating the exact WHERE clause of one of the unioned statements. Jonathan Lewis posted a followup to say “Oracle can be very touchy about how it plays this game” and made a prediction of how the CBO would handle a slightly different scenario.

This was the extra scenario and I include brief details on creating the unioned view too. NB all on Oracle 11.2.0.2. {non-Exadata :-) }

Exclusion of Unioned SQL in Views?

Question – you have a view definition of the following format:

select 1 as d_type, col_a,col_b,col_c
from TAB_X, TAB_Y, TAB_Z
where {your predicates}
UNION
select 2 as d_type, col_a,col_b,col_c
from TAB_P, TAB_Q, TAB_R
where {your predicates}
UNION
select 3 as d_type, col_a,col_b,col_c
from TAB_X X, TAB_Y, TAB_Z
where {your predicates}

You now select from the view and your code includes a filter predicate such as:

“WHERE D_TYPE = 1″

SQL Challenges

June 14, 2012 Dominic Delmolino put together a very interesting challenge.  The challenge is to produce something called a Pascal matrix using Oracle Database… more specifically, just SQL.  I had a vague recollection of Pascal matrixes when I read Dominic’s challenge.  Basically, the goal is to create a matrix similar to the following: The rule [...]

Shrinking Tables to Aid Full Scans

{This blog is about shrinking tables where the High Water Mark is higher than it needs to be. Prompted by one of the comments, I wrote a follow-up post on finding the High Water Mark and tables that consist mostly of empty space, which would be candidates for shrinking.}

This blog is about one of those things I do as almost an autonomous “not thinking about it” performance housekeeping task, one which I have been meaning to mention for ages.

There can be quite a lot to gain by checking out full scans on “small” tables and seeing if it is as efficient as it can be. Sometimes it is, sometimes it is not. Often it is “good enough”. Occasionally it is awful.

Recently I was just casting an eye over the “top 20″ SQL on a system for any code generating a lot of consistent gets. I came across the below:

Reproducing a Canned Report using a Single SQL Statement

April 11, 2012 I recently received an interesting request for assistance from an ERP email mailing list.  The author of the email wanted to reproduce a canned report found in the ERP package so that the information could be published on a Microsoft Sharepoint system.  The author of the email is using SQL Server for [...]

Monitoring Changes to Table Data

March 22, 2012 Suppose that you receive a request stating that a particular table in one of your databases must be monitored for changes.  One such table might be the one that lists the ERP system’s suppliers and their addresses – you would not want someone to be able to set up a legitimate supplier, and later [...]

V$SQL.IS_OBSOLETE

The column is there for a long time – even 9i documentation have it. I’ve never thought about it until today when I caought something extraordinary on 11.2.0.3 instance.

Starting with 10g oracle introduced SQL_ID for simplicity; it is used in combination with CHILD_NUMBER to locate a particular row in the V$SQL. The documentation is clear (bold is mine):

V$SQL lists statistics on shared SQL areas without the GROUP BY clause and contains one row for each child of the original SQL text entered