A shortcut notation for the JOIN operator when both columns have the same name:

select o.customer_id, o.order_date, p.product_name
from orders o
  join products p using (customer_id); 

is equivalent to

select o.customer_id, o.order_date, p.product_name
from orders o
  join products p on o.customer_id = p.customer_id;

The USING operator also removes duplicate columns if * is used in the SELECT list:

select *
from orders o
  join products p on o.customer_id = p.customer_id;

The column customer_id will only occur once in the above result.

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