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?
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...)
Oracle 12c introduced the ability to specify sequence.nextval as the default on a column, which is really nice – including the fact that it eliminates one of your excuses why you don’t decommission those old triggers.
Unfortunately it doesn’t work as you might expect if you use an
INSERT ALL statement; it evaluates the default expression once per statement, instead of once per row.
create sequence test_seq; create table test_tab ( id number default (more...)
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?
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...)
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
Oracle Database Release 12c (12.1) introduced a new operator that we can use in SQL queries. The MATCH_RECOGNIZE operator allows us to detect patterns in our relational data. Specifically: it allows us to identify records that mark the beginning of a set of records that together form a pattern. In this set, each record satisifies a certain condition. The fact that in a set of records these conditions are met – in a certain (more...)
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
Let’s start with explaining a bit what table functions are. Table Functions are functions that return a collection of (more...)
One of those things SQL developers are frequently looking at is the generation of rows: having a query return records that do not really exist. For example to generate test data or to produce records for all days in a month. Tom Kyte usually selects from data dictionary views. Various tricks make the rounds, for example based on CONNECT BY or CUBE or UNPIVOT. This blog article by Natalka Roshak (2015) compares various row generation (more...)
What is an ANTI-JOIN? And what is the difference between the SEMI-JOIN and the ANTI-JOIN?
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...)
email@example.com > create table t( pk int primary key check(pk > 0)); Table created. firstname.lastname@example.org > insert /*+ignore_row_on_dupkey_index(t(pk)) */ into t email@example.com > select trunc(dbms_random.value(1, 1e5)) from dual firstname.lastname@example.org > connect by level <= 1e5 email@example.com > / 63187 rows created.
Finding the first n gaps
firstname.lastname@example.org > variable n number email@example.com > exec :n := 1000 PL/SQL procedure successfully completed. firstname.lastname@example.org > set autotr (more...)
Could you tell me what the difference is between NVL and COALESCE?
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...)
I have got a website with a search form. I want to display a limited number of results to the user and have him/her navigate through different pages. Is this possible using plain SQL?
Of course this is possible. It might take some thinking, but that has never hurt anyone (yet). First we need a table with some randomly sorted data in it. In this example I (more...)
Even though a space is a regular character, the client didn't want spaces at the beginning or end of a string. Any spaces in the middle were fine.
Of course this could be handled by the application, but it must also be implemented in the database. Using a check constraint with a regular expression will prevent the end user from entering unwanted data.
To try things out, let's just start with a simple table with (more...)
SQL> conn andrew/reid
SQL> create table tab1 as
2 select table_name from dba_tables
Because my hero is Cary Millsap, I'm going to do what he did and publish my
Brendan Tierney and (more...)
Today a box arrived from Oracle Press. In it were a few copies of “Real-World SQL and PL/SQL” which I co-authored with Arup Nanda, Brendan Tierney, Heli Helskyaho and Alex Nuitjen. I know I only blogged about the book a couple of weeks back, how I became involved and the impact it had on my life for several months, but as I can now physically handle and read (more...)
I’ve just added a picture to the right side of this site. It is for a book about SQL and PL/SQL. If you look at the image of the front cover, at the bottom is a list of authors and, near the end, is my name. It’s all finished and at the printers, but it is not out yet – It should be published in the next few weeks.
The British part of me wants (more...)