emp, MySQL - rextester

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drop table if exists employees;

create table if not exists employees (emp_id int, emp_name varchar(100), job varchar(100), mgr int, hire_date date, sal int);

insert into employees values
(7369, 'Smith', 'Clerk', 7902, '20101217', 1800),
(7499, 'Allen', 'Salesman', 7698, '20110220', 2600),
(7521, 'Ward', 'Salesman', 7698, '20110222', 2250),
(7566, 'Jones', 'Manager', 7839, '20110402', 3975),
(7654, 'Martin', 'Salesman', 7698, '20110928', 2250),
(7698, 'Blake', 'Manager', 7839, '20110501', 3850),
(7782, 'Clark', 'Manager', 7839, '20110609', 3450),
(7788, 'Scott', 'Analyst', 7566, '20121209', 4000),
(7839, 'King', 'CEO', 0, '20111112', 6000),
(7844, 'Turner', 'Salesman', 7698, '20110808', 2500),
(7876, 'Adams', 'Clerk', 7788, '20130112', 2100),
(7900, 'James', 'Clerk', 7698, '20111203', 1950),
(7902, 'Ford', 'Analyst', 7566, '20111203', 4000),
(7934, 'Miller', 'Clerk', 7782, '20120123', 2300);

select   x.emp_id,
         x.emp_name, 
         x.job,
         x.mgr,
         x.hire_date,
         x.sal,
         (select   group_concat(y.emp_id)
          from     employees y
          where    y.hire_date < x.hire_date
          and      y.sal < x.sal
          order by y.hire_date desc) prev_emp_id
from     employees x
order by x.emp_id;

drop table if exists employees;


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