How to get Latest N Records of selected Group - mysql

Question

I want to run a query on MySql version 5.1.9 that returns me only top two (order by JoiningDate) of selected Dept.
For example, my data is like:
+-------+------------------------------------------+----------+------------+
| empid | title | Dept | JoiningDate|
+-------+------------------------------------------+----------+------------+
| 1 | Research and Development | 1 | 2015-08-06 |
| 2 | Consultant | 2 | 2015-08-06 |
| 3 | Medical Consultant | 3 | 2015-08-06 |
| 4 | Officer | 4 | 2015-08-06 |
| 5 | English Translator | 5 | 2015-08-06 |
| 6 | Teacher | 1 | 2015-08-01 |
| 7 | Physical Education | 2 | 2015-08-01 |
| 8 | Accountant | 3 | 2015-08-01 |
| 9 | Science Teacher | 4 | 2015-08-01 |
| 10 | Home Science | 5 | 2015-08-01 |
| 11 | Research Assistant | 1 | 2015-08-05 |
| 12 | Consultant | 2 | 2015-08-05 |
| 13 | Consultant HR | 3 | 2015-08-05 |
| 14 | Technical Lead | 4 | 2015-08-05 |
| 15 | Hindi Translator | 5 | 2015-08-05 |
| 16 | Urdu Teacher | 1 | 2015-08-02 |
| 17 | Physical Education | 2 | 2015-08-02 |
| 18 | Accountant | 3 | 2015-08-02 |
| 19 | Science | 4 | 2015-08-02 |
| 20 | Home Science | 5 | 2015-08-02 |
+-------+------------------------------------------+----------+------------+
I want the query to output the latest joined two empid's of Dept (1,2,3) i.e:
+-------+------------------------------------------+----------+------------+
| empid | title | Dept | JoiningDate|
+-------+------------------------------------------+----------+------------+
| 1 | Research and Development | 1 | 2015-08-06 |
| 11 | Research Assistant | 1 | 2015-08-05 |
| 2 | Consultant | 2 | 2015-08-06 |
| 12 | Consultant | 2 | 2015-08-05 |
| 3 | Medical Consultant | 3 | 2015-08-06 |
| 13 | Consultant HR | 3 | 2015-08-05 |
+-------+------------------------------------------+----------+------------+

Answer 1

In mysql you can use user defined variables to achieve you desired results
SELECT
t.empid,
t.title,
t.Dept,
t.JoiningDate
FROM
(
SELECT
*,
#r:= CASE WHEN #g = b.Dept THEN #r + 1 ELSE 1 END rounum,
#g:= b.Dept
FROM (
SELECT *
FROM table1
CROSS JOIN (SELECT #r:= NULL,#g:=NULL) a
WHERE Dept IN(1,2,3)
ORDER BY Dept,JoiningDate DESC
) b
) t
WHERE t.rounum <=2
DEMO

Answer 2

Use a correlated sub-select to count number of rows with same date but a later JoiningDate. If less than 2, return the row.
select empid, title, Dept, JoiningDate
from tablename t1
where (select count(*) from tablename t2
where t2.Dept = t1.Dept
and t2.JoiningDate > t1.JoiningDate) < 2

Answer 3

Query
select *
from emp_ t1
where
(
select count(*) from emp_ t2
where t2.Dept = t1.Dept
and t2.JoiningDate > t1.JoiningDate
) <= 1
and t1.Dept in (1,2,3)
order by t1.Dept;
SQL Fiddle
Can also achieve it by giving a rownumber.
Query
select t2.empid,
t2.title,
t2.Dept,
t2.JoiningDate
from
(
select empid,
title,
Dept,
JoiningDate,
(
case Dept
when #curA
then #curRow := #curRow + 1
else #curRow := 1 and #curA := Dept end
) as rn
from employee t,
(select #curRow := 0, #curA := '') r
where Dept in (1,2,3)
order by Dept,JoiningDate desc
)t2
where rn < 3;
SQL Fiddle