Skip to main content

How many rows fit into DUAL?

Let's consider the contents of the famous dual table:

SQL>select * from dual;

D
-
X

SQL>select rownum from dual;

ROWNUM
----------
1

Now let's try to get multiple rows returned form dual:


SQL>select rownum from dual connect by rownum < = 5;

ROWNUM
----------
1

So there's still one row, whichs results in a rownum of 1. Now let's ask the max of rownum:

SQL>select max(rownum) from dual connect by rownum < = 5;

MAX(ROWNUM)
-----------
5

Kinda strange isn't it? Now let's try to get these 5 rows:

SQL>select * from (select rownum from dual connect by rownum < = 5);

ROWNUM
----------
1
2
3
4
5

Another strange feature is that in TOAD

select rownum from dual connect by rownum < = 5

returns 5 rows (and in SQL*Plus only one as you can see above).

Does this kind of behaviour also occurs on other tables/views?
In my application I've got one materialized view, so a select from all_mviews returns one row (just like dual):

SQL>select count(*) from all_mviews;

COUNT(*)
----------
1

SQL>select rownum from all_mviews;

ROWNUM
----------
1

SQL>select rownum from all_mviews connect by rownum< =5;

ROWNUM
----------
1
2
3
4
5

SQL>select rownum from dual connect by rownum< =5;

ROWNUM
----------
1

So the one row from dual behaves different than the one row from all_mviews....

So what you see is what you get, but what you get is not what you have!

Comments

Anonymous said…
eh???

SQL*Plus: Release 10.2.0.2.0 - Production on Thu Apr 16 16:11:21 2009

Copyright (c) 1982, 2005, Oracle. All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning and Data Mining options

SQL> select rownum from dual connect by rownum < = 5;

ROWNUM
----------
1
2
3
4
5

SQL>

Popular posts from this blog

Fix Interactive Report headers issue when using a Region Display Selector

When you have multiple Interactive Reports (IR) on your page and use a Region Display Selector to mimic tabs, you might notice some weird behaviour in the IR headings if you switch tabs. The headings are not positioned correctly and you get an extra empty row under the headings. It just looks weird and ugly. But if you resize your browser window, it all looks fine again (until you switch to another tab..) So can we fix this by creating a Dynamic Action that mimics that "browser window resize" event? Yes we can! Create a Dynamic Action that fires on Click of the jQuery selector li.apex-rds-item a . That should fire a JavaScript snippet :  apex.event.trigger(this.triggeringElement, "apexwindowresized"); So now a click on a tab not only switches from one IR to another but also fires that event that will "autofix" the IR headers. A simple solution for an annoying problem. This applies to APEX 5.0, I assume it will be solved in 5.1.

How to create neatly formatted Excel documents using PL/SQL?

If there is a requirement to produce output from an application into Excel, you would probably create a CSV (Comma Separated File) with the data and start Excel to show the data - at least that's what I did...until now. The drawback of this solution is that you could only produce data and no nice layout. But Excel is also capable of opening HTML-files and using this you could create Excel files with data and magnificent layout! Let me give an example: 1. Create a procedure to show the data in formatted in an HTML table. CREATE OR REPLACE PROCEDURE display_emp_list IS v_emp_count NUMBER(5); v_empno NUMBER(8); v_ename VARCHAR2(50); v_job emp.job%TYPE; v_sal emp.sal%TYPE; v_bg_color VARCHAR2(10) := ''; CURSOR c_emp IS SELECT empno, initcap(ename), job, sal FROM emp ORDER BY ename; BEGIN SELECT COUNT(*) INTO v_emp_count FROM emp; owa_util.mime_header('application/ms-excel', FALSE); htp.p('Content...

APEX ReadOnly Pages - The easy way

If your Oracle APEX Application requires different types of access - full access or readonly - for different types of users, you can specify a Read Only Condition on Page level (or Region, Item, Button, etc.).  You can set an Authorization Scheme on Application level, so it'll be applied to all pages. So if you have an Authorization Scheme named 'User Can Access Page' defined by a PL/SQL function like this: return apex_authorization.user_can_access_page ( p_app_id  => :APP_ID , p_page_id => :APP_PAGE_ID , p_user    => :APP_USER );  then you can code all the logic in the database using the APEX Repository, your own tables or a combination to define whether a user has access to that page or not. But alas it is not possible to define something similar Application wide for a Read Only condition. You can specify an Authorization Scheme 'User has Read Only Access' using a similar signature as the one above and use that on each and e...