共有四个表
topic user teacher student
CREATE TABLE student(
student_id INT AUTO_INCREMENT NOT NULL,
student_name VARCHAR(80) NOT NULL,
student_number VARCHAR(20) NOT NULL,
student_photopath VARCHAR(50) ,
PRIMARY KEY(student_id)
);
CREATE TABLE teacher(
teacher_id INT AUTO_INCREMENT NOT NULL,
teacher_name VARCHAR(80) NOT NULL,
teacher_number VARCHAR(80) UNIQUE NOT NULL,
teacher_photopath VARCHAR(50) ,
PRIMARY KEY(teacher_id)
);
CREATE TABLE user(
user_id INT AUTO_INCREMENT NOT NULL,
target ENUM('1','0') NOT NULL, -- 身份标识(学生:1 老师:0)
user_number VARCHAR(80) UNIQUE NOT NULL,--学生或老师的账号
PRIMARY KEY(userlogin_id)
)
CREATE TABLE topic(
topic_id INT AUTO_INCREMENT NOT NULL,
topic_title VARCHAR(300) NOT NULL, -- 话题标题
topic_content TEXT NOT NULL, -- 话题内容
user_number VARCHAR(20) NOT NULL, -- 话题创建人账号
PRIMARY KEY(topic_id)
) ;
我的需求是这样的要查询 topic_id,topic_title,topic_content , user_number
,user_name,user_photopath(user_name和user_photopath,是student或者teacher表中的),需要根据user表中的target判断一下具体去哪个表中查,这样的查询语句怎么写。不知道我说清楚了没,这个问题困惑了好久,求大神解答