insert if not exists oracle

Question

I need to be able to run an Oracle query which goes to insert a number of rows, but it also checks to see if a primary key exists and if it does, then it skips that insert.

Answer 1

The statement is called MERGE. Look it up, I'm too lazy.

Beware, though, that MERGE is not atomic, which could cause the following effect (thanks, Marius):

SESS1:

create table t1 (pk int primary key, i int);
create table t11 (pk int primary key, i int);
insert into t1 values(1, 1);
insert into t11 values(2, 21);
insert into t11 values(3, 31);
commit;

SESS2: insert into t1 values(2, 2);

SESS1:

MERGE INTO t1 d
USING t11 s ON (d.pk = s.pk)
WHEN NOT MATCHED THEN INSERT (d.pk, d.i) VALUES (s.pk, s.i);

SESS2: commit;

SESS1: ORA-00001