How Can Get Random 2 rows FROM EACH GROUP FROM JOINED TABLE
Answer to the new question:

SELECT `dept_name`
    , `emp_name`
    , `emp_sal`
    , `ej_joining date`
FROM (
    SELECT emp.`dept_name`, emp.`emp_name`, emp.`emp_sal`, emp.`ej_joining date`
        , @num := IF(@dept_id = `emp_dept_id`, @num +1, 1) as num
        , @dept_id := `emp_dept_id` as `dept_id`
    FROM (
        SELECT DT.`dept_name` 
            , EMP.`emp_name`, EMP.`emp_sal`, EMP.`emp_dept_id`
            , EJ.`ej_joining date`
        FROM `Dept` DT 
        INNER JOIN `Employee` EMP ON DT.`dept_id` = EMP.`emp_dept_id`
        INNER JOIN `JoiningDate` EJ ON EJ.`ej_emp_id` = EMP.`emp_id`
        WHERE DT.`dept_status` = '1' AND EMP.`emp_status` = '1' 
        ORDER BY Dt.`dept_id`, RAND()
    ) emp
    CROSS JOIN (
        SELECT @dept_id := 0 as dept_id, @num := 0 as num
    ) v
) num 
WHERE num.num &lt;= 2
ORDER BY `dept_name`, num.num
;


SQL Fiddle



This answers the original question



This first query will randomly order rows by dept_id. Each row in each group of dept_id is given a incremental number (num) from 1 to n.

Random order query:

SELECT `emp_name`, `emp_sal`
        , @num := IF(@dept_id = `emp_dept_id`, @num +1, 1) as num
        , @dept_id := `emp_dept_id` as `emp_dept_id`
FROM (
    SELECT `emp_name`, `emp_sal`, `emp_dept_id`
    FROM `Employee`
    ORDER BY emp_dept_id, RAND()
) emp
CROSS JOIN (
    SELECT @dept_id := 0 as dept_id, @num := 0 as num, @numx := 0 as numx
) v


The Dept table can then be joined to this query. A filter on num value being 1 or 2 will give the first 2 rows of each dept_id. SQL Fiddle
The order changes for each execution and the first 2 rows change as well.

Main query:

SELECT DT.`dept_name`, num.`emp_name`, num.`emp_sal`
FROM `DEPT` DT 
INNER JOIN (
    SELECT `emp_name`, `emp_sal`
            , @num := IF(@dept_id = `emp_dept_id`, @num +1, 1) as num
            , @dept_id := `emp_dept_id` as `emp_dept_id`
    FROM (
        SELECT `emp_name`, `emp_sal`, `emp_dept_id`
        FROM `Employee`
        ORDER BY emp_dept_id, RAND()
    ) emp
    CROSS JOIN (
        SELECT @dept_id := 0 as dept_id, @num := 0 as num
    ) v
) num 
    ON DT.`dept_id` = num.`emp_dept_id`
WHERE num.num &lt;= 2
ORDER BY  DT.`dept_name`, num.num