Question

这是应该从表中删除学生的代码。但它不起作用。它只在表名是静态时才有效。

public function delete_student($student_class,$school_session,$id){
    $table_name = $student_class."_".$school_session."_student_record";
    $pdo = KITE::getInstance('pdo');
    $query = $pdo->prepare("DELETE FROM ".$table_name." WHERE `id` = ?");
    $query->bindValue(1,$id);
    $query->execute();

}

Answer 1

正如我在评论中提到的，在表格，列，函数名称，过程名称等的名称中不允许使用斜杠/。为什么在名称静态输入时您的查询有效是一个谜。

快速构建的演示，使用innodb表foreign keys，希望很少/没有冗余。如果您在本地运行mysql，请尝试在您的gui中运行它（例如https://support.google.com/googleplay/android-developer/answer/140504?hl=en），以了解它是如何完成的。

drop database if exists `demo_school_sessions`;
create database if not exists `demo_school_sessions`;
use `demo_school_sessions`;


drop table if exists `classes`;
create table if not exists `classes` (
  `id` int(10) unsigned not null auto_increment,
  `class` varchar(50) not null,
  primary key (`id`)
) engine=innodb default charset=latin1;

insert into `classes` (`id`, `class`) values
    (1, 'mathematics'),
    (2, 'physics'),
    (3, 'computing');


drop table if exists `sessions`;
create table if not exists `sessions` (
  `id` int(10) unsigned not null auto_increment,
  `session` varchar(50) not null,
  primary key (`id`)
) engine=innodb default charset=latin1;

insert into `sessions` (`id`, `session`) values
    (1, 'summer'),
    (2, 'winter'),
    (3, 'spring'),
    (4, 'autumn');

drop table if exists `students`;
create table if not exists `students` (
  `id` int(10) unsigned not null auto_increment,
  `student` varchar(50) not null,
  primary key (`id`)
) engine=innodb default charset=latin1;

insert into `students` (`id`, `student`) values
    (1, 'bobby droptables'),
    (2, 'sue select'),
    (3, 'david delete'),
    (4, 'valerie view'),
    (5, 'peter procedure'),
    (6, 'freddy function');

drop table if exists `year`;
create table if not exists `year` (
  `id` int(10) unsigned not null auto_increment,
  `year` varchar(9) not null default '2014/2015',
  primary key (`id`)
) engine=innodb default charset=latin1;

insert into `year` (`id`, `year`) values
    (1, '2014/2015'),
    (2, '2015/2016'),
    (3, '2016/2017'),
    (4, '2017/2018'),
    (5, '2018/2019'),
    (6, '2019/2020');

drop table if exists `master`;
create table if not exists `master` (
  `id` int(10) unsigned not null auto_increment,
  `student` int(10) unsigned not null default '0',
  `class` int(10) unsigned not null default '0',
  `session` int(10) unsigned not null default '0',
  `year` int(10) unsigned not null default '0',
  primary key (`id`),
  key `student` (`student`),
  key `class` (`class`),
  key `session` (`session`),
  key `year` (`year`),
  constraint `fk_year` foreign key (`year`) references `year` (`id`) on delete cascade on update cascade,
  constraint `fk_class` foreign key (`class`) references `classes` (`id`) on delete cascade on update cascade,
  constraint `fk_session` foreign key (`session`) references `sessions` (`id`) on delete cascade on update cascade,
  constraint `fk_stud` foreign key (`student`) references `students` (`id`) on delete cascade on update cascade
) engine=innodb default charset=latin1;

insert into `master` (`id`, `student`, `class`, `session`, `year`) values
    (1, 1, 3, 4, 1),
    (2, 1, 1, 4, 1),
    (3, 2, 2, 4, 1),
    (4, 2, 3, 4, 1);


/* example to select records */
select * from `master` m
  left outer join `students` s on s.id=m.student
  left outer join `classes` c on c.id=m.class
  left outer join `sessions` ss on ss.id=m.`session`
  left outer join `year` y on y.id=m.`year`
where m.`class`=3 or m.`student`=1;

/* Example to delete a student */
delete from `students` where `id`=1;


/*

*/

由于Foreign Key Dependencies，如果您从学生表中删除学生，master表中的所有相关记录也将被删除，因为cascade设置了update }和delete。使用这样的foreign keys时必须小心，因为如果您意外删除了一条记录，并且该密钥上有一个级联删除集，那么所有相关记录都会消失！

手动编码的表名称有效，但动态名称在PHP中不起作用

1 个答案: