mysql: command to remove all blank spaces from records

gistfile1

UPDATE
    accounts_table
INNER JOIN
    customers_table ON (accounts_table.user_id = customers_table.user_id)
SET 
    accountnumber = RTRIM(accountnumber)
WHERE
    customers_table.customer_id = 'customer id';

If you do not have many records in accounts_table, and you want to make sure that all the accountnumber values are trimmed, you can simply apply the trim to all the records as follows:

UPDATE
    accounts_table
SET 
    accountnumber = TRIM(accountnumber);