GROUP_CONCAT within CONCAT

Question

Database hierarchical structure is as follow

• Student Name
  • List of fee Assigned to Each Student
    • List of Scholarship Assigned to Each Fee

As structure, expected output is

Student Name-Fee->Scholarship1, Scholarship2

Karan-1.Annual Fee->Economic Scholarship,Incapable Scholarship,2.Monthly Fee 

But what I am getting

Student Name-Fee->Scholarship1, Student Name-Fee->Scholarship2

Karan-1.Annual Fee->Economic Scholarship,1.Annual Fee->Incapable Scholarship,2.Monthly Fee

What is wrong in here ? Though I am nesting CONCAT , but not getting expected output

CONCAT(student.en_ttl,'-',GROUP_CONCAT(DISTINCT fee.id,'.',fee.en_ttl,
    COALESCE(CONCAT('->',sch.en_ttl),''))) AS fee

SQL Fiddle

Answer 1

You basically need to two levels of GROUP BY . So, we will need to use a Derived Table here. First subquery will aggregate at the level of fee ; and then the second level would aggregate those fee details at the level of student .

Also, in newer (and ANSI SQL compliant) versions of MySQL, you need to ensure that any non-aggregated column in the SELECT clause should be in the GROUP BY clause as well.

Query

SELECT
  CONCAT(stud_ttl,'-',GROUP_CONCAT(CONCAT(fee_det, COALESCE(CONCAT('->',fee_sch), '')))) AS fee
FROM 
(
  SELECT  student.ttl AS stud_ttl, 
        CONCAT(fee.id,'.',fee.ttl) AS fee_det,   
        Group_concat(DISTINCT sch.ttl) AS fee_sch 
  FROM   inv_id
       JOIN student
         ON student.id = inv_id.std
       JOIN inv_lst
         ON inv_lst.ftm = inv_id.ftm
       JOIN fee
         ON fee.id = inv_lst.fee
       JOIN sec_fee
         ON sec_fee.fee = fee.id
            AND sec_fee.cls = student.cls
            AND sec_fee.sec = student.sec
       LEFT JOIN std_sch
              ON std_sch.std = student.id
       LEFT JOIN sec_sch
              ON sec_sch.sch = std_sch.sch
                 AND sec_sch.fee = fee.id
       LEFT JOIN sch
              ON sch.id = sec_sch.sch
  GROUP  BY student.ttl, fee_det, fee.ttl
) dt
GROUP BY stud_ttl;

Result

| fee                                                                  |
| -------------------------------------------------------------------- |
| Karan-1.Annual->Economic Scholarship,Incapable Scholarship,2.Monthly |

---

View on DB Fiddle