MySQL 创建主键,外键和复合主键的语句

MySQL 创建主键，外键和复合主键的方法，需要的朋友可以参考下。

1.创建主键语法文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

ALTER TABLE table_name ADD CONSTRAINT pk_name PRIMARY KEY(列名);文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

2.创建外键语法文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

ALTER TABLE news_info[子表名] ADD CONSTRAINT FK_news_info_news_type[约束名] FOREIGN KEY (info_id)[子表列] REFERENCES news_type[主表名] (id)[主表列] ;文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

3.使用组合主键文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

如果一列不能唯一区分一个表里的记录时，可以考虑多个列组合起来达到区分表记录的唯一性，形式文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

①创建时：create table sc (文章源自很文博客https://www.hinven.com很文博客-https://www.hinven.com/47937.html

studentno int,

courseid int,

score int,

primary key (studentno,courseid) );

②修改时：alter table tb_name add primary key (字段1,字段2,字段3);