（1）定义客户表customer、供应商表supplier、商品信息表goods、订单信息表order、信誉等级表creditgrade和商品类型表goodstype的主键。

（2）定义以上各表的外键约束。

（3）定义惟一约束：customer表的loginname字段；supplier表的loginname字段和suppliername字段；creditgrade表的creditgradename字段；goodstype表的goodstypename字段。

-(1) The definition of customer Table customer, vendor table supplier, Information Table commodity goods, orders information table order, creditgrade credibility scales and the type of commodity goodstype table of the main keys. (2) definition of the above table outside the key constraint. (3) defines the only constraint : the customer table loginname field; supplier table loginname field and suppliername field; creditgrade table creditgradename field; goodstype table goodstypename field.