Truncating LISTAGG prior to 12.2

I've been following the LISTAGG problem for a while because I find the function useful.

The problem being this error:
ORA-01489: result of string concatenation is too long

It relates to when the result set is over 4000 characters, eg:
with data as (select rpad('x',400, 'x') str from dual connect by level <=10)
select listagg(str,', ') within group (order by null)
from data
Ten rows of 400 characters equals 4000, add the concatenation operator and you get (more...)

Formatting results from ORE script in a SELECT statement

This blog post looks at how to format the output or the returned returns from an Oracle R Enterprise (ORE), user defined R function, that is run using a SELECT statement in SQL.

Sometimes this can be a bit of a challenge to work out, but it can be relatively easy once you have figured out how to do it. The following examples works through some scenarios of different results sets from a user defined (more...)

Script: Inactive Parallel QC Holding Parallel Processes

Working on a data warehouse system can be quite challenging, as I mentioned in the post from yesterday. One of the things we need to take care of is the amount of parallel processes that are in used at all times. Yesterday I wrote about how to locate downgraded sessions. Today we will look at another aspect – who “steals” parallel processes and what can we do to solve it.

One of the biggest thieves (more...)

Script: Finding Session With Downgraded Parallel Execution

I was working with the data warehouse team at a customer site and at some point we realized that some parallel executions are not getting enough resources (downgraded).

Not getting enough parallel processes in such a complex environment is really bad. That means that since everybody is hogging the CPU, some sessions will not be able to complete inside the night ETL time frame. If that happens – some ETLs will go on into the (more...)

Explicit Semantic Analysis setup using SQL and PL/SQL

In my previous blog post I introduced the new Explicit Semantic Analysis (ESA) algorithm and gave an example of how you can build an ESA model and use it. Check out this link for that blog post.

In this blog post I will show you how you can manually create an ESA model. The reason that I'm showing you this way is that the workflow (in ODMr and it's scheduler) may not be for everyone. (more...)

Explicit Semantic Analysis in Oracle 12.2c Database

A new Oracle Data Mining algorithm in the Oracle 12.2c Database is called Explicit Semantic Analysis.

[The following examples are built using Oracle Data Miner 4.2 (SQL Developer 4.2) and the Oracle 12.2 Database cloud service (extreme edition) ]

The Explicit Semantic Analysis algorithm is an unsupervised algorithm used for feature extraction. ESA does not discover latent features but instead uses explicit features based on an existing knowledge base. There (more...)

A Recipe for Summoning the RBO Monster (even in Oracle 12c): On Delete Cascade, Function-Based Index and Missing Table Statistics

The last version of Oracle in which CHOOSE was officially supported as an OPTIMIZER_MODE parameter value was 9.2.
This is what the documentation of Oracle 9.2 says about it:

The optimizer chooses between a cost-based approach and a rule-based approach based on whether statistics are available.
If the data dictionary contains statistics for at least one of the accessed tables, then the optimizer uses a cost-based approach and optimizes with a goal (more...)

Inserting data in SQL*Plus correctly

When inserting data into the database, it is occasionally forgotten (especially by English-speakers) that we need to take steps to ensure we are inserting data correctly and without unexpected character translation.

For example, in SQL*Plus we need to ensure we set the NLS_LANG environment variable to the correct setting for our database before we initiate SQL*Plus.

Here’s a quick example showing what can go wrong:

[oracle@ORA122 ~]$ echo $NLS_LANG

[oracle@ORA122 ~]$ sqlplus neil/neil
SQL*Plus: Release  (more...)

SQL Developer: Quick Outline with SQL statements

Most of you probably know the "Quick Outline" function you have inside the SQL Developer.
It helps you to easily jump between different functions/procedures inside a package.

My colleague Holger told me about a bug in SQL Developer 3.x where you could use the "Outline" view with normal SQL files, too. Unfortunately in version 4 it didn't work anymore. So he stayed with version 3 for a long while. Otherwise he would had to (more...)

Answer with SQL: How many weekdays a year?

I'm a big fan of generating data with dual, using a perk of the connect by syntax.

I think Tom Kyte was the originator of this technique. It's not necessarily the fastest method, but it's super convenient - no table required.

Today I wanted to know how many weekdays a year, so I defined 365 rows on the fly using sysdate to turn these into each day of the year. Then I ran a simple (more...)

Tablespaces verkleinern (TEMP, USER_TS, ORA-03297)

Die Select-Statements in diesem Blogpost habe ich von anderen Webseiten kopiert. Daher ist dieser Beitrag eher als Zusammenfassung unterschiedlicher Lösungsversuche zu sehen und dient mir als schnelle Hilfe bei der Verkleinerung eines zu großen Tablespaces. Schaut euch die Quellen an, die sehr viel detaillierter auf die jeweiligen Probleme eingehen.

Wer kennt nicht die Situation? Der DBA ruft an und meint der TEMP Tablespace verbraucht mehrere hundert Gigabyte an Speicher.

Was ist in solch einer (more...)

A handful of articles

A little while ago a member of the Danish Oracle User Group DOUG asked if anyone had a bit of experience with use of R together with Oracle Database. I remembered an article I wrote for OTech Magazine on forecasting with R and Oracle and thought it would be a good primer for him. OTech Magazine is no longer active, sadly, but I thought I could send him a link anyway to my article. That (more...)

How can we use Oracle to deduplicate our data

Dear Patrick,

We have gone through a merger at our company where we are trying to merge the databases. The problem now is that we have duplicate records in our tables. We can of course go through all the records by hand and check if they exist twice. Another option is to build an application to do this. But using the Oracle Database there must be a better way to do this. Any ideas?

Ramesh (more...)

OTN Appreciation Day: Analytic Functions

This is my contribution to the OTN Appreciation Day, which was initiated by Tim Hall.

One of my favorite features of the Oracle Database are Analytic Functions. They were introduced with Oracle Database 8.1.6 Enterprise Edition, and have been in the Standard Edition since version 9.

With analytic functions you can add inter-row calculations, aggegrate over multiple dimensions, rank assignments based on values. All this without a GROUP BY clause.
The syntax might (more...)

What is overloading and how and when do I use it

Dear Patrick,

Recently I heard someone talk about overloading in Java. What is it, is it possible in PL/SQL and if so, how would I use it?

Ramesh Cumar

Dear Ramesh,

Overloading is a technique of creating multiple programs with the same name that can be called with different sets of parameters. It is definitely possible to apply this technique in PL/SQL, in fact, Oracle does this a lot of times in their own built-in (more...)

Celebrate Batman Day with SQL

Because today is Batman Day, it calls for a celebration of the SQL type:

SQL> select listagg (b)
2 within group (order by null) ||' Batman'
3 from (select 0f/0 b
4 from dual
5 connect by level <= 14
6 );

NanNanNanNanNanNanNanNanNanNanNanNanNanNan Batman

When would you use a normal table function?

Dear Patrick,

Last year I did a presentation on table functions at KScope. One of the questions I got was: ‘If pipelined table functions provide their results faster, why would you want to use a normal table function?’ I couldn’t come up with the answer then, maybe you can help?

Erik van Roon

Dear Erik,

Let’s start with explaining a bit what table functions are. Table Functions are functions that return a collection of (more...)

What’s the difference between SEMI-JOIN and ANTI-JOIN?

Dear Patrick,

What is an ANTI-JOIN? And what is the difference between the SEMI-JOIN and the ANTI-JOIN?

Lillian Sturdey

Dear Lillian,

First of all, both SEMI-JOIN and ANTI-JOIN are not in the SQL syntax but they are more a pattern. You might expect to be able to write something like:

[PATRICK]SQL>SELECT d.deptno, d.dname, d.loc
               FROM dept d
               SEMI JOIN emp e ON (e.deptno = d.deptno)

to get all the (more...)

Find first n gaps in integer primary key


sokrates@12.1 > create table t( pk int primary key check(pk > 0));

Table created.

sokrates@12.1 > insert /*+ignore_row_on_dupkey_index(t(pk)) */ into t
sokrates@12.1 > select trunc(dbms_random.value(1, 1e5)) from dual
sokrates@12.1 > connect by level <= 1e5 
sokrates@12.1 > /

63187 rows created.

Finding the first n gaps

sokrates@12.1 > variable n number
sokrates@12.1 > exec :n := 1000

PL/SQL procedure successfully completed.

sokrates@12.1 > set autotr  (more...)

What is the difference between NVL and COALESCE?

Dear Patrick,

Could you tell me what the difference is between NVL and COALESCE?

Kindest regards,
Paul McCurdey

Dear Paul,

NVL returns the value of the first argument if it doesn’t evaluate to NULL, otherwise it will return the value of the second argument.
COALESCE returns the first argument that doesn’t evaluate to NULL. That can be any one of the arguments.
So they are definitely similar – but there are significant differences.
First of (more...)