Thread: cluster index on primary key

Hi there,

I'd like to know when I create a primary key on a table, does postgres will 
create automatically an index on that table related to the primary key 
columns, or I have to create it explicitly ?

If I have to create it explicitly, suppose I have tables with a serial 
primary key, or link tables with multiple column primary key. How is 
recommended for the two cases: to create an index on the primary key unique, 
or cluster or both or with none of the two options ?

TIA,
Sabin 

On 6/11/07, Sabin Coanda <sabin.coanda@deuromedia.ro> wrote:
> I'd like to know when I create a primary key on a table, does postgres will
> create automatically an index on that table related to the primary key
> columns, or I have to create it explicitly ?

From http://www.postgresql.org/docs/8.2/static/indexes-unique.html :

"PostgreSQL automatically creates a unique index when a unique
constraint or a primary key is defined for a table. The index covers
the columns that make up the primary key or unique columns (a
multicolumn index, if appropriate), and is the mechanism that enforces
the constraint."