SQL 从 3 个表中获取所需结果的查询

Question

架构

CREATE TABLE IF NOT EXISTS `exams` (
  `id` int(6) unsigned NOT NULL,
  `name` varchar(100) NOT NULL,
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `institutions` (
  `id` int(6) unsigned NOT NULL,
  `name` varchar(100) NOT NULL,
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `exam_scores` (
  `id` int(6) unsigned NOT NULL,
  `exam_id` int(6) NOT NULL,
  `institution_id` int(6) NOT NULL,
  `score` int(5)
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;

INSERT INTO `exams` (`id`, `name`) VALUES
  ('1',  'exam1'),
  ('2',  'exam2'),
  ('3',  'exam3'),
  ('4',  'exam4');
  ('5',  'exam5');

INSERT INTO `institutions` (`id`, `name`) VALUES
  ('1',  'institution1'),
  ('2',  'institution2'),
  ('3',  'institution3'),
  ('4',  'institution4');
  ('5',  'institution5');

INSERT INTO `exam_scores` (`id`, `exam_id`, `institution_id`, `score`) VALUES
  ('1',  '1', 1, 40),
  ('2',  '2', 1, 45),
  ('3',  '3', 2, 35),
  ('4',  '1', 2, 30);
  ('5',  '4', 3, 40);

现在用户将输入exm1

我正在尝试创建查询以查找如下所示的所有相关考试。查找匹配输入 exm1 的考试，同时查找匹配机构 inn exam_scores table.

中存在的其他考试

例1：输入exm4

desired output
| exm4 |

例2：输入exm3

desired ouput 
| exm3 |
| exm1 |

例3：输入exm1

desired output 
| exm1 |
| exm2 |
| exm3 |

到目前为止，我只提出了一个只给出匹配考试的查询:)

select exams.name from exams
inner join exam_scores on exam_scores.exam_id = exams.id
// ??
where exams.id = 1

Answer 1

您可以使用 joins 执行此操作：

select distinct e1.name
from exams e1
inner join exam_scores es1 on es1.exam_id = e1.id
inner join exam_scores es2 on es2.institution_id = es1.institution_id
inner join exams e2 on e2.id = es2.exam_id
where e2.name = ?

Answer 2

我建议使用变量，因为它允许您使用 SET 操作轻松更新变量的值（例如，如果您的用户将要使用 GUI）。

在下面的代码中，您只需将 exm1 值更改为所需的值即可。

declare @input nvarchar(10);
set @input = 'exm1';

select distinct a.name
from exams a
   inner join exam_scores b on b.exam_id = a.id
   inner join exam_scores b2 on b2.institution_id = b.institution_id
   inner join exams a2 on a2.id = b2.exam_id
where a2.name = @input

SQL 从 3 个表中获取所需结果的查询

SQL query for getting desired result from 3 tables

mysql

sql

join

inner-join

where-clause