MYSQL data type changes without affecting existing table foreign key costraints

 create table CUSTOMER (
        CUSTOMER_ID BIGINT NOT NULL,
        CUSTOMER_NAME VARCHAR(255) NOT NULL UNIQUE,
        CONTACT_PERSON VARCHAR(255) NOT NULL,
        CUSTOMER_EMAIL VARCHAR(255) NOT NULL,
        ADDRESS VARCHAR(255),
        CITY VARCHAR(255),
        PHONE VARCHAR(255),
        FAX VARCHAR(255),

        constraint...