sql server 2005 - Change primary key to a nullable column without losing data -

i have table in have data.

i have primary key on column, want change column rencently added. added column nullable, updated able make not null.

i used

alter table mytable modify termdefid int not null 

but receive error

incorrect syntax near 'modify'.

after want (after drop current pk, of course) :

alter table [dbo].[mytable] add  constraint [pk_mytable] primary key clustered  (     [termdefid] asc )with (pad_index  = off, statistics_norecompute  = off, sort_in_tempdb = off, ignore_dup_key = off, online = off, allow_row_locks  = on, allow_page_locks  = on, fillfactor = 90) on [primary] go 

i not able make new column not null. problem. how can this?

i use sql server 2005, maybe problem!

in sql server, primary key column(s) cannot nullable

also: alter table command invalid sql server - should be:

alter table mytable  alter column termdefid int not null 

but again: if column part of primary key, it cannot nullable.

see relevant msdn documentation on primary key constraints:

a table can have 1 primary key constraint, , a column participates in primary key constraint cannot accept null values. because primary key constraints guarantee unique data, defined on identity column.