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

If you do NOT want to merge in from an other table, but rather insert new data... I came up with this. Is there perhaps a better way to do this?

MERGE INTO TABLE1 a
    USING DUAL
    ON (a.C1_pk= 6)
WHEN NOT MATCHED THEN
    INSERT(C1_pk, C2,C3,C4)
    VALUES (6, 1,0,1);

Answer 2

It that code is on the client then you have many trips to the server so to eliminate that.

Insert all the data into a temportary table say T with the same structure as myFoo

Then

insert myFoo
  select *
     from t
       where t.primary_key not in ( select primary_key from myFoo) 

This should work on other databases as well - I have done this on Sybase

It is not the best if very few of the new data is to be inserted as you have copied all the data over the wire.

Answer 3

This only inserts if the item to be inserted is not already present.

Works the same as:

if not exists (...) insert ... 

in T-SQL

insert into destination (DESTINATIONABBREV) 
  select 'xyz' from dual 
  left outer join destination d on d.destinationabbrev = 'xyz' 
  where d.destinationid is null;

may not be pretty, but it's handy :)

Answer 4

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