Re: how to add primary key to existing table with multiple

On Thu, 23 Feb 2006, Daniel Joo wrote:

> I am trying to add another primary key to an existing table with two
> other primary keys.  I got the following error when I tried this
> command:

You only can have one primary key.  The table you gave has a single
primary key with two columns.  Are you trying to guarantee that expid
along is unique or that the set (probeid, tissueid, expid) is unique?

You can make expid UNIQUE and NOT NULL for the first case which is similar
to a primary key (although it's not a default foreign key target).  In the
second you can drop the current constraint and add one on the three
columns.

> Indexes:
>
>     "extprobe2tissue_pkey" PRIMARY KEY, btree (probeid, tissueid)
>     "extprobe2tissue_probeid" btree (probeid)
>     "extprobe2tissue_tissueid" btree (tissueid)