Question

如何让一个老师的所有学生，每个学生有一个老师，每个老师有很多学生，我正在使用此SQL请求，每个老师只有一个学生，您能帮忙吗

   $data = '';
          $sth = Model::connect()->prepare('SELECT a.name ,
          b.nameTeacher 
          FROM table1 b , table2 a
         WHERE a.id_teacher = b.id GROUP BY b.id');
               $sth->execute();
                 $data = $sth->fetchAll();


        return $data;

表1

老师：

Id

nameTeacher

表2

学生：

Id

名称

Id_teacher

Answer 1

删除GROUP BY，并学习使用正确，明确的标准 JOIN语法：

SELECT a.name, b.nameTeacher 
FROM table1 b JOIN
     table2 a
     ON a.id_teacher = b.id ;

Answer 2

这将起作用：

select a.name,b.nameTeacher from students a ,teacher b
where a.Id_teacher=b.Id

Answer 3

SELECT b.nameTeacher, count(a.name) as numberOfStudents
      FROM table1 b , table2 a
     WHERE a.id_teacher = b.id GROUP BY b.id

或：

 SELECT a.Id, a.name
      FROM table1 b , table2 a
     WHERE a.id_teacher = b.id and (b.id = [input ID] or b.nameTeacher = [input name]

如何获取带有外键的表的倍数值？

3 个答案: