Question: I have a table with two number columns, and a unique constraint over them both. I would like to insert a new pair of values UNLESS the pair already exists. What is the simplest way to do this?

If I do 

```
insert into TABLE values (100,200) 

```

and the pair already exists I get a ORA-00001 error, so I would like to do something like 

```
insert or update into TABLE values (100,200)

```

Answer: 
You can use [MERGE](http://psoug.org/reference/merge.html)
You can try something like:

```
insert into table
select :a, :b from dual
where not exists (select 1 from table where column1 = :a and column2=:b)

```