mysql 移除前两字符串

UPDATE users SET username = SUBSTRING(username, 3);

UPDATE users SET username = REPLACE(LEFT(username, LENGTH(username) - 2), '', '');

UPDATE users SET username = 
    CASE 
        WHEN LENGTH(username) > 2 THEN SUBSTRING(username, 3)
        ELSE username
    END;

UPDATE users SET username = 
    CASE 
        WHEN LENGTH(username) > 2 THEN SUBSTRING(username, 3)
        ELSE username
    END,
    phone_number = 
        CASE 
            WHEN LENGTH(phone_number) > 2 THEN SUBSTRING(phone_number, 3)
            ELSE phone_number
        END;