sql 中的 Group_Concat 多列

Question

I have two tables.

First table is called Employee

  |EID| EName|  Salary |
=========================
  |1  |A     |300      |
  |2  |B     |400      | 
  |3  |O     |500      |

Second table is called Employee_Sal_Changes

  |EID|  Salary_Change_History| year
=======================================
  |1  |100                    |2012
  |1  |200                    |2013
  |1  |300                    |2014
  |2  |200                    |2013 
  |2  |400                    |2014 
  |3  |100                    |2011
  |3  |200                    |2012
  |3  |300                    |2013
  |3  |500                    |2014

On my front end table, I would like to show

 id   |Salary Change History    |
=================================
 A    | 100:2012                |
      | 200:2013                |
      | 300:2014                |
=================================
 B    | 200:2013                |
      | 400:2014                |
=================================
 O    | 100:2011                |
      | 200:2012                |
      | 300:2013                |
      | 400:2014                |
=================================

I would like to get salary_change_history and year mached to EID and show them on the front end by using loop.

To get those, I tried to store them in an array by using group_concat but it only gets values where EID = 1

Here is the query in the backend

Select 
(select Group_Concat(Employee_Sal_Changes.Salary_Change_History),(Group_Concat(Employee_Sal_Changes.year) from Employee_Sal_Changes left join Employee on Employee_Sal_Changes.EID = Employee.EID), 
Employee.EName
From Employee_Sal_Changes

Is there a better way or just keep using group_concat?

Answer 1

You can use aggregation:

select 
    eid, 
    group_concat(
        year, ':', salary_change_history 
        order by year
        separator '\n'
    ) salary_change_history
from employee_sal_changes
group by eid

For each employee, this generates a list of <year>:<salary> values separated by carriage returns. Note that you don't need to bring in the employee table to generate that resultset: the other table has all necessary information.

Demo on DB Fiddle :

---

If you want the employee name as well:

select 
    s.eid, 
    e.ename,
    group_concat(
        s.year, ':', s.salary_change_history 
        order by s.year
        separator '\n'
    ) salary_change_history
from employee_sal_changes s
inner join employee e on e.eid = s.eid
group by s.eid, e.ename