unique key problem on update

Hi folks.

I've got the table and data shown below. 

I want to add a new page after page 2 so I try to increase the sequence number 
of each row from page 3 onwards to make space in the sequence for the new 
record. However, I get duplicate key errors when I try. Can anyone suggest 
how I get round this.

Also, the final version will be put onto a WordPress web site which means I 
will have to port it to MYSQL which I don't know, so any solution that will 
work with both systems would be a great help.

Ta

Gary


stainburn=# \d skills_pages                                   Table "public.skills_pages"  Column    |         Type
    |                          Modifiers                           
 
-------------+-----------------------+--------------------------------------------------------------sp_id       |
integer              | not null default 
 
nextval('skills_pages_sp_id_seq'::regclass)sp_sequence | integer               | not nullsp_title    | character
varying(80)| sp_narative | text                  | 
 
Indexes:   "skills_pages_pkey" PRIMARY KEY, btree (sp_id)   "skills_pages_sequence" UNIQUE, btree (sp_sequence)

stainburn=# select * from skills_pages;sp_id | sp_sequence |     sp_title     | sp_narative 
-------+-------------+------------------+-------------    1 |          10 | Departments      |     2 |          20 |
InterestGroups  |     3 |          30 | Customer Focused |     4 |          40 | Business Roles   |     5 |          50
|Commercial       |     6 |          60 | People Oriented  |     7 |          70 | Engineering      | 
 
(7 rows)

stainburn=# update skills_pages set sp_sequence=sp_sequence+10 where 
sp_sequence >= 30;
ERROR:  duplicate key value violates unique constraint "skills_pages_sequence"
stainburn=#