Fourth International NoCOUG SQL Challenge

The Fourth International NoCOUG SQL Challenge has been published in the May issue of the NoCOUG Journal available at Shakespeare’s story of Romeo and Juliet plays out in an American setting. In the NoCOUG version, Romeo sings American songs to Juliet and gives her gourmet dipped swizzled strawberries for her birthday. The bard of Avon must be rolling in his grave.

Entries should be attached as a comment to this announcement. (more...)

LoggerUtil: Create a Custom Template

Since I have written about my pet project about a month ago, I have made some major changes to the functionality of it.
If you haven't read that blog about my pet project, here's the synopsis:

I love Logger to instrument my code, I just don't like to type in all the bits and pieces to register all the input arguments when I write a new procedure or function. To solve this problem I have (more...)

Strategies for Minimising SQL Execution Plan Instability

Execution Plan Instability – What is the problem?

The Oracle Optimizer is a complex piece of software and with every release it becomes more complex.


In the beginning, the Optimizer was rule-based.

The Optimizer had a ranked list of heuristics used to optimize a query, picking the lowest ranked rule available.

This rule-based mode, whilst still in use with some internal Oracle dictionary queries, has been unsupported since version 10.1.

This means that (more...)

Little quiz: Ordering/Grouping – Quess the output

How many times have you guessed the right answer? :)

select * from dual order by -1;
select * from dual order by 0;


select *                   from dual                                     order by -(0.1+0/1) desc;
select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by -(0.1+0/1) desc;


select 1 n,0 n,2 n,0 n,1 n from dual group by grouping sets(1,2,3,2,1,0) order by 0;
select 1 n,0 n,2  (more...)

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 37: POISED: A problem-solving method

P.O.I.S.E.D. is the acronym I invented for the performance tuning method described by Chris Lawson in The Art and Science of Oracle Performance Tuning; it stands for Problem, Observation, Interpretation, Solution, Execution, and Documentation. The Observation and Interpretation phases feed each other. The Interpretation phase concludes with a determination of root cause. If we are investigating poor performance a single SQL statement, the tool of choice for the observation phase (more...)

Overview of all time changes this year via SQL

inspired by Laurent Schneider’s remark concerning special time changes in Lord Howe Island

with dates as
trunc(sysdate, 'year') + level - 1 as day
connect by
extract(year from trunc(sysdate, 'year') + level - 1) = extract(year from trunc(sysdate, 'year'))

timezones as
vtn.TZNAME, listagg(vtn.TZABBREV, ', ') within group(order by vtn.tzabbrev) tzabbrevs
v$timezone_names vtn
group by

offsets as
v.*, d. (more...)

What’s this ‘WHERE 1=1′?

Since some time I have been adding WHERE 1=1 to all my queries.
I get queries like this:

  FROM emp e
 WHERE 1=1
   AND e.ename LIKE 'A%'
   AND e.deptno = 20

Lots of people ask me what’s the use of this WHERE 1=1.

You know I like to type as little as possible but here I am typing a lot of extra characters. And yet, it makes my development life a (more...)

Join Tables on Date Ranges

A recent question on the OTN SQL forum asked how best to join two tables related by ID and date range, in order to insert one row per date into a data warehouse. One solution was to expand the data from each table, creating one row per date, then join on date. I think it's more efficient to join on date range, then expand.

Visualizing Statspack Performance Data in SQL Developer

If you run Oracle Standard Edition or haven’t licenced Diagnostics Pack for Enterprise Edition, then you don’t have AWR and ASH Data available. This is when Statspack, the predecessor of AWR, comes in handy to keep a history of database performance metrics. But although Oracle still deliver Statspack with their recent DB releases (yes, even in […]


In this post I will try to show you how I used the Oracle Apex and the APEX_WEB_SERVICE  PL/SQL package to quickly send a request to a public Internet API and how I handled the response. The code below was written during a 'Hackday' and hasn't been extensively tested.

My use case is integrating Oracle Apex with the public Mendeley REST API for Mendeley Catalog Search.

The idea was to build an (more...)

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 36: The sisters of the mother of all SQL antipatterns

The mother of all SQL “anti-patterns” is the ad-hoc query. Here, the end-user of the application can specify any combination of parameters—for example, the job_id, the dept_id, or a combination of both—and the data is retrieved using a catchall query. This antipattern has two sisters who are almost as evil. These two sisters arise from the requirement to paginate through the records retrieved by a query.(read more)

Comparing NULLable Values

If a column or expression may be NULL, it is a pain to compare it to something else. Why? Because comparisons involving a NULL do not result in TRUE or FALSE: they result in NULL. I use the DECODE function to work around this problem: here's why - and how.

To N or Not to N, is SYS_OP_C2C the Question; Oracle NVARCHAR Slow?

February 8, 2015 I was recently contacted about an odd performance issue with a software product named TDM, where certain SQL statements submitted to an Oracle 9.2.x database required roughly 30 seconds to execute when a nearly instantaneous response was expected.  The person who reported the issue to me provided a sample SQL statement that […]

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 35: Robust v/s optimal query execution plans

A subset of all possible execution plans can be described as robust. While such solutions are not always quite optimum, they are almost always close to optimum in real-world queries, and they have desirable characteristics, such as predictability and low likelihood of errors during execution.(read more)

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 34: SQL Aaargh!

The biggest problem with SQL query optimization is that semantically equivalent SQL queries are not guaranteed to perform equally well. When I encounter problems like this, I sympathize with the folks who got frustrated with RDBMS performance and created NoSQL.(read more)

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 33: The mother of all SQL antipatterns?

The mother of all SQL “anti-patterns” is the ad-hoc query. Here, the end-user of the application can specify any combination of parameters—for example, the job_id, the dept_id, or a combination of both—and the data is retrieved using a catchall query.(read more)

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 32: Pretzels created by someone experimenting with hallucinogens?

In an interview for the NoCOUG Journal, Steven Feuerstein said: “Some people can perform seeming miracles with straight SQL, but the statements can end up looking like pretzels created by someone who is experimenting with hallucinogens.” As if to prove Steven correct, NoCOUG held three international SQL challenges. The winning entries were mind-boggling indeed.(read more)

Share your interesting SQL or PL/SQL experience on stage, on camera, or in print

If you have had interesting experiences with SQL or PL/SQL in your career, here’s your opportunity to share them on stage, on camera, or in print. Send your stories to and we’ll forward them to the SQL evangelists team headed up by Steven Feuerstein. You may be selected to tell your stories on stage at the YesSQL! presentation at the winter conference next Tuesday or your stories may be recorded on camera or (more...)

How to avoid a salted banana! (SQL tuning)‏

Dear NoCOUG members and friends,

You’re going to enjoy the new issue of the NoCOUG Journal. Click here to download it.

  • Lothar Flatz talks about the biggest issue in SQL tuning: the “salted banana.” We predict that the phrase “salted banana” will become as widely known in the Oracle community as “compulsive tuning disorder.” Click here to go directly to Lothar’s article.
  • Janis Griffin—a.k.a. the Looney Tuner—explains why the Oracle (more...)

MySQL Locking

Have you ever wondered if MySQL does Row Level Locking? Or wondered why are you getting the error:

ERROR 1205 (HY000) : Lock wait timeout exceeded; try restarting transaction

You get the error because your allocated time to hold a DML lock in a transaction exceeds the set limit. Usually the default limit to hold a DML row lock, set by innodb_lock_wait_timeout db parameter, is 50 seconds. If your transaction doesn't commit/rollback within 50 seconds (more...)