DUPLICATE FIX 2

You can make sure that you do not insert duplicate information by using the EXISTS condition.
For example, if you had a table named clients with a primary key of client_id, you could use the following statement:

INSERT INTO clients(client_id, client_name, client_type)
SELECT supplier_id, supplier_name, 'advertising'
FROM suppliers
WHERE not exists (select * from clientswhere clients.client_id = suppliers.supplier_id);

This statement inserts multiple records with a subselect.
If you wanted to insert a single record, you could use the following statement:

INSERT INTO clients(client_id, client_name, client_type)
SELECT 10345, 'IBM', 'advertising'
FROM dual
WHERE not exists (select * from clientswhere clients.client_id = 10345);

The use of the dual table allows you to enter your values in a select statement, even though the values are not currently stored in a table.