例如：QQ表 ?與 ?QQ的基本信息 表，一個(gè)QQ表中只能對應(yīng)一個(gè)昵稱或者簽名详民，一個(gè)信息表中只能對應(yīng)一個(gè)QQ賬戶
????????CREATE TABLE QQ(
????????????????qqid INT PRIMARY KEY,?
????????????????PASSWORD VARCHAR(50)
????????);
????????CREATE TABLE QQDetail(
????????????????qqid INT PRIMARY KEY, -- 添加主鍵讓其值不為空
????????????????NAME VARCHAR(50),
????????????????address VARCHAR(200)
????????);
????ALTER TABLE QQDetail ADD CONSTRAINT fk_QQ_QQDetail_qqid FOREIGN KEY (qqid) ?REFERENCES QQ(qqid);
