Oracle Problem from a beginner

From: Chung Wing Tat Áéºa¹F <jliuws_at_hkstar.com>
Date: 1997/11/16
Message-ID: <64mdg6$2673@lyra.hkstar.com>#1/1

Hello every body!

I am a beginner of Oracle in Hong Kong, I have a table which structures are listed as follows:

   ref_no varchar(8)
   date_from date
   date_to date

I need to setup a constraint to this table to ensure that there is no overlapping date range in all rows so I want to setup following constraint just example ) :

alter table booking

      add constraint CHECK_DOBULE_BOOKING check ( not (


       ( date_to   < ( select date_from from booking ) ) and

       ( date_from > ( select date_to   from booking ) ) ) )

I was prompted that Oracle doesn't support sub-query in this case. how can I do it by table constraint? and how can I distinguish the field between the newly added one and the one already inside the table when setup a constraint?

Chung Wing Tat
wtchung_at_writeme.com

16-Nov-1997 Received on Sun Nov 16 1997 - 00:00:00 CST