Comments on: Oracle’s Dual Table

By: lkeria

lkeria — Mon, 21 Jun 2010 14:54:32 +0000

You can also use the DUAL table tu test the avaibality of the database. Select 1 from dual;

By: ymonette

ymonette — Mon, 21 Jul 2008 16:42:23 +0000

Select sex
from (table name)
order by sex ASC;

This will separate M from F

Otherwise if you want just M (or just F)

Select sex
from (table name)
where sex = ‘M’;

By: goutam

goutam — Sun, 20 Jan 2008 14:10:32 +0000

hi
its a beautiful sight,my question is iam haveing a column named sex

in which a subdivsion male and female catgeory is there and i have

some memers underit how can i retrive the male and female seperately

in a single statment.

By: Norman

Norman — Thu, 10 Jan 2008 15:02:33 +0000

Along with Dov Wasserman, author of comment #5, I wonder how the name “Dual” was selected. We might ask where the name was first used and who were the contributors. Let’s keep looking for an answer.

Good luck!

Norman

By: Bernd Eckenfels

Bernd Eckenfels — Sat, 24 Nov 2007 00:57:59 +0000

Some Application Servers use the “select ‘X’ from DUAL;” dummy statement to verify the ORacle Connection is working. This used to make lots ofproblems because that table got quite “hot”. This is why Oracle 10g has a special Optimizer for this Table.

Greetings
Bernd

By: Dov Wasserman

Dov Wasserman — Fri, 24 Aug 2007 15:27:55 +0000

I find it amusing that the table explicitly created for the purpose of having one row is called dual. Anyone happen to know why that name was chosen? I’m sure there’s some interesting historical etymology. Well, interesting to some of us database + word geeks.

By: Jon Emmons

Jon Emmons — Fri, 13 Apr 2007 22:27:21 +0000

Twingle, Sorry for the delayed response. You can actually select all sorts of things from any table. Try this: select 4+3, sysdate, 'some text' from user_tables; The values will be repeated for every record in user_tables. Basically these values aren't selected from the table, but are rather provided as constant values, independent of the table contents. It's a bit tricky, but this functionality allows us to format the output like in the following (which also uses the double-pipe concatenate operator):

select 'The user ' || username || ' has a status of ' || account_status
from dba_users;

'THEUSER'||USERNAME||'HASASTATUSOF'||ACCOUNT_STATUS
--------------------------------------------------------------------------------
The user MDSYS has a status of EXPIRED & LOCKED
The user ORDSYS has a status of EXPIRED & LOCKED
The user EXFSYS has a status of EXPIRED & LOCKED
The user DMSYS has a status of EXPIRED & LOCKED
The user DBSNMP has a status of OPEN
The user SCOTT has a status of OPEN

Hope this helps.

By: Twingle

Twingle — Tue, 10 Apr 2007 06:03:02 +0000

Duel table is having a column “DUMMY” and its of type VARCHAR2(1).How it can return sysdate,which always have size greater than VARCHAR2(1)? Anybody having an idea about this?…

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