MySQL Select 查询以根据列表值获取记录

Question

我正在使用 MySQL。我有 3 Table 如下。

Table : subject_Master

--------------------------
subjectId   | subjectShortName
----------------------------------
1           |   English
2           |   French
3           |   German
4           |   Latin
----------------------------------

Table : class_Master

-----------------------------------
classId     | className
----------------------------------
1           |   Rose
2           |   Dasy
3           |   Lily

Table：主题分配

------------------------------------------
allocationId    |   classId |   subjectId
-------------------------------------------
1               |   1       |   1,2
2               |   2       |   2,3,4
3               |   3       |   1,2,3,4

如何获得如下 SQL 结果，想要为 subjectAllocation 行中的每个 subjectId 获取 SubjectName

ClassName   |   SubjectName
-------------------------------------------
Rose        |   English,French
Dasy        |   French,German,Latin
Lily        |   English,French,German,Latin

Answer 1

使用FIND_IN_SET()函数：

试试这个：

SELECT A.allocationId, 
       B.className, 
       GROUP_CONCAT(C.subjectShortName) AS subjectName
FROM subjectAllocation A
INNER JOIN class_Master B ON A.classId = B.classId 
INNER JOIN subject_Master C ON FIND_IN_SET(C.subjectId, A.subjectId) 
GROUP BY A.allocationId;

Answer 2

计划

fix subjectAllocation so it is accessible & linkable

use sequence generator ( from digits_v ) to unroll variable length string into structured data

access the structured data in simple way, joining on indexed fields

设置

create table subject_Master
(
  subjectId integer primary key not null,
  subjectShortName varchar(23) not null
);

create table class_Master
(
  classId integer primary key not null,
  className varchar(23) not null
);

create table subjectAllocation_inaccessible
(
  allocationId integer primary key not null,
  classId integer not null,
  subjectId varchar(32) not null,
  foreign key ( classId ) references class_Master ( classId )
);

create table subjectAllocation
(
  allocationId integer primary key not null,
  classId integer not null,
  subjectId integer not null,
  foreign key ( classId ) references class_Master ( classId ),
  foreign key ( subjectId ) references subject_Master ( subjectId )
);

insert into subject_Master
( subjectId, subjectShortName )
values
( 1           ,   'English' ),
( 2           ,   'French'  ),
( 3           ,   'German'  ),
( 4           ,   'Latin'   )
;

insert into class_Master
( classId, className )
values
( 1           ,   'Rose' ),
( 2           ,   'Dasy' ),
( 3           ,   'Lily' )
;

insert into subjectAllocation_inaccessible
( allocationId, classId, subjectId )
values
( 1               ,   1       ,   '1,2'      ),
( 2               ,   2       ,   '2,3,4'    ),
( 3               ,   3       ,   '1,2,3,4'  )
;

修复主题分配

create view digits_v
as
SELECT 0 AS N 
UNION ALL 
SELECT 1 
UNION ALL 
SELECT 2 
UNION ALL 
SELECT 3 
UNION ALL 
SELECT 4 
UNION ALL 
SELECT 5 
UNION ALL 
SELECT 6 
UNION ALL 
SELECT 7 
UNION ALL 
SELECT 8 
UNION ALL 
SELECT 9
;

insert into subjectAllocation
( allocationId, classId, subjectId )
select @row_number := @row_number + 1 as allocationId, sa.classId, substring_index(substring_index(sa.subjectId, ',', n.n), ',', -1) sub
from subjectAllocation_inaccessible sa
cross join
(
  select a.N + b.N * 10 + 1 n
  from digits_v a
  cross join digits_v b
  order by n
) n
cross join ( select @row_number := 0 ) params
where n.n <= 1 + (length(sa.subjectId) - length(replace(sa.subjectId, ',', '')))
;

访问的简单性

select c.className, group_concat(s.subjectShortName)
from subjectAllocation sa
inner join class_Master c
on sa.classId = c.classId
inner join subject_Master s
on sa.subjectId = s.subjectId
group by c.className
;

此处连接到 class_Master 可以使用主索引 ( subjectId )

输出

+-----------+----------------------------------+
| className | group_concat(s.subjectShortName) |
+-----------+----------------------------------+
| Dasy      | French,German,Latin              |
| Lily      | German,Latin,English,French      |
| Rose      | English,French                   |
+-----------+----------------------------------+

sqlfiddle

参考

SO mysql sequence generator
junction tables
SO How to store arrays in mysql
database normalisation

MySQL Select 查询以根据列表值获取记录

MySQL Select query to fetch record base on list values

mysql

sql

select

group-concat

find-in-set