关于MySQL通配符的问题

[SQL-木子Lee]

有一个自然连接查询语句
select c.*,o.order_num,o.order_date,oi.prod_id,oi.quantity,oi.item_price
from customers as c,orders as o, orderitems as oi
where c.cust_id = o.cust_id and oi.order_num = o.order_num and prod_id = 'FB';
问题：其中的c.*是什么意思，为什么 这么用？
给出查询涉及的表字段
CREATE TABLE customers
(
cust_id int NOT NULL AUTO_INCREMENT,
cust_name char(50) NOT NULL ,
cust_address char(50) NULL ,
cust_city char(50) NULL ,
cust_state char(5) NULL ,
cust_zip char(10) NULL ,
cust_country char(50) NULL ,
cust_contact char(50) NULL ,
cust_email char(255) NULL ,
PRIMARY KEY (cust_id)
) ENGINE=InnoDB;


CREATE TABLE orderitems
(
order_num int NOT NULL ,
order_item int NOT NULL ,
prod_id char(10) NOT NULL ,
quantity int NOT NULL ,
item_price decimal(8,2) NOT NULL ,
PRIMARY KEY (order_num, order_item)
) ENGINE=InnoDB;


CREATE TABLE orders
(
order_num int NOT NULL AUTO_INCREMENT,
order_date datetime NOT NULL ,
cust_id int NOT NULL ,
PRIMARY KEY (order_num)
) ENGINE=InnoDB;