在left join SQL之后更改列值

SELECT column1, column2, ... FROM left_table LEFT JOIN right_table ON left_table.column = right_table.column;

SELECT customers.customer_id, orders.order_id, orders.total_amount
FROM customers
LEFT JOIN orders ON customers.customer_id = orders.customer_id;

customer_id | order_id | total_amount
------------|----------|--------------
1           | 100      | 50.00
2           | NULL     | NULL
3           | 101      | 20.00

UPDATE orders
SET total_amount = 0
WHERE total_amount IS NULL;

customer_id | order_id | total_amount
------------|----------|--------------
1           | 100      | 50.00
2           | NULL     | 0.00
3           | 101      | 20.00