Mysql 建表时设置多个主键

CREATE TABLE `Student`(
    `s_id` VARCHAR(20) primary key,
    `s_name` VARCHAR(20) ,
    `s_birth` VARCHAR(20) ,
    `s_sex` VARCHAR(10) 
)engine = Innodb default charset = utf8mb4 ;

CREATE TABLE `Teacher`(
    `t_id` VARCHAR(20),
    `t_name` VARCHAR(20),
    PRIMARY KEY(`t_id`)
)engine = Innodb default charset = utf8mb4;

CREATE TABLE `Score`(
    `s_id` VARCHAR(20) ,
    `c_id`  VARCHAR(20) ,
    `s_score` INT(3),
    PRIMARY KEY(`s_id`,`c_id`)
)engine = Innodb default charset = utf8mb4;