Help with MySQL

[Jander]

I am designing a website for school using MySQL as a backend. I have a customer table and a payment table. The Customer table has the fields.

Customer_ID which is primary key and autoincrement
and other fields

Then I have a Payment table which has the fields
Account_ID which is primary key and autoincrement
Customer_ID which is Unique key

In phpmyadmin Relation view I have Customer_ID in the payment table linked to Customer_ID in the Customer table.

Now I want the Customer_ID from the Customer table to populate the Customer_ID field from the payment table. How do I accomplish that?

[the_Igel]

insert into payment (customer_id) select customer_id from customer

but it seems you're trying to dosomething extremely useless. Why customer_id in payment is unique? one customer should pay only once? Then you can merge two tables in one, asyou don't need to store customers separately from payments.