Insert into table if second table has conditional value

Question

I have two tables:

Table 1 (customers)

customer_id   customer_name  salesPerson_id
1             John           1
2             Ed             1
3             Sam            2

Table 2 (customerContacts)

contact_id   customer_id  phone_number
1            1            687-5309
2            1            555-1234
3            1            742-1111

I am trying to let only the sales person add / update a phone number for their specific customer.

So only sales salesPerson_id 1 could update John and Ed and only salesPerson_id 2 could update Sam.

I believe I am looking for something like:

INSERT INTO customerContacts (contact_id , customer_id , phone_number) VALUES (1 , 1 , '987-6543')
ON DUPLICATE KEY UPDATE phone_number='987-6543'
    IF customers.salesPerson_ID = 1

But it doesn't seem like sql supports if statements.

Answer 1

INSERT INTO customerContacts (contact_id , customer_id , phone_number) 
    Select 1 , customer_id , '987-6543' 
    from customers
    where salesPerson_ID = 1 and customer_id=1;

This is the query which you should use in the native way but you need to fit this in your application framework