Initialize a new row in my table (MySql) [closed]
id_customers    order
       1          1
       1          2
       1          3
       2          1
       2          2
       2          3
       3          1
       3          2
       3          3

SET @counter = 1;
SET @last = 0;
UPDATE table SET order = (IF(@last = customer_id,@counter + 1,@counter := 1)),
                 @last := customer_id
ORDER BY customer_id

SELECT * FROM customers ORDER BY `id_customers` ASC, `order` ASC