Dont Insert duplicate rows

Hi, I need to insert rows into table1 from table2 and table3 but I don't want to insert repeated combinations of col2, col3. So, table1 has the primary key col2, col3.

This the table1:

create table table1(
col1 int not null,
col2 int not null,
col3 int not null,
constraint PK_table1 primary key (col2, col3)
)

This is my "insert" code:

INSERT INTO table1
SELECT table2.col1,table2.col2, table3.col3
FROM table2, table3
WHERE table2.col1 = table3.col1

Wich conditions shoud i add to this code?

Thanks.

fmilano.If Col2 and Col3 is controlled by Primary key then it will be taken care and if any data is added will be errored.|||To be erroed is what I want to avoid. So, I want to filter this rows by columns col2 and col3.