How to insert record only if primary key does not exist

Table is defined as

 

CREATE TABLE firma1.klient (

  kood character(12) NOT NULL DEFAULT nextval('firma1.klient_kood_seq'::regclass),

....

);

 

How to insert record to this table only if primary key does not exist ?

I tried code below but got strange error as shown in log file.

Why this error occurs ?

 

Andrus.

 

2012-06-30 15:51:04 EEST ERROR:  duplicate key value violates unique constraint "klient_pkey"

2012-06-30 15:51:04 EEST DETAIL:  Key (kood)=(20037       ) already exists.

2012-06-30 15:51:04 EEST STATEMENT:  insert into klient (

    kood,

    nimi,

    tanav,

    piirkond,

    postiindek

    )

    select ((E'20037')), ((E'Statoil Fuel & Retail')), ((E'')), ((E'10148 nnn')),((E''))

    from klient

    where not exists (select 1 from klient where kood =((E'20037')))