MySQL：判断逗号分隔的字符串中是否包含某个字符串 && 如何在一个以逗号分隔的列表中的一个字段中连接MySQL中的多对多关系中的数据

需求：
      sql语句中，判断以逗号分隔的字符串中是否包含某个特定字符串，类似于判断一个数组中是否包含某一个元素，

      例如：判断 ’a,b,c,d,e,f,g‘ 中是否包含 'a'，sql语句如何实现？

解决
   1、mysql 字符串函数判断：   FIND_IN_SET(ele, str)  

     ele 是一个特定字符，

     str 是一个以逗号分隔的字符串 或者 匹配这个参数的字段，必须以逗号分隔

select * from t_user where FIND_IN_SET('26', '1,26');

//ids： 以逗号分割的字符串
select * from t_user where FIND_IN_SET('26', ids);
   FIND_IN_SET() 函数返回该字符串所在的位置，如果不存在就返回0,

2、ORDER BY FIND_IN_SET() 可以用来排序。

   如果想让 id 按 30 27 29 排序

select * from t_user where id in(30,27,29) order by FIND_IN_SET(id,'30,29,27');
   

二 原文

I have a many-to-many relationship between People and Departments since one person can be in many departments.

People          Departments
------          -----------
pID  pName      deptID   deptName
1    James      1        Engineering
2    Mary       2        Research
3    Paul       3        Marketing
                4        Communications

People_Departments
------------------
pID   deptID
1     1
1     2
2     2
2     4
3     1
3     2
3     3

What I want is this:

pName  deptName
James  Engineering, Research
Mary   Research, Communication
Paul   Engineering, Research, Marketing

If I do plain LEFT JOINs on the tables using the SQL below, I will get several rows related to one person:

SELECT people.pName,
       departments.deptName
FROM people
LEFT JOIN people_departments ON people.pID=people_departments.pID
LEFT JOIN departments ON people_departments.deptID=departments.deptID

I have tried various combinations of GROUP_CONCAT but without luck.

Any ideas to share?

解决

 SELECT people.pName,
           GROUP_CONCAT(departments.deptName SEPARATOR ', ') deptName
      FROM people
 LEFT JOIN people_departments 
        ON people.pID = people_departments.pID
INNER JOIN departments 
        ON people_departments.deptID = departments.deptID
  GROUP BY people.pID

Output:

+-------+----------------------------------+
| pName | deptName                         |
+-------+----------------------------------+
| James | Engineering, Research            |
| Mary  | Research, Communications         |
| Paul  | Engineering, Research, Marketing |
+-------+----------------------------------+
3 rows in set (0.00 sec)

（转载https://blog.csdn.net/qq_42402854/article/details/88030469  &&  https://www.it1352.com/1475016.html）