Sql SELECT for personnel available in a specific time period - sql

Question

I have 3 tables. First one is a list of personnel:
Table Personnel
Id_personnel Name
1 John
2 Alice
3 Tom
4 Charles
5 Ben
Second is a table with medical leave:
Table Medical
Id_personnel Start_date End_date
3 2012-08-02 2012-08-05
2 2012-08-02 2012-08-15
4 2012-10-04 2012-10-06
2 2012-10-02 2012-10-15
2 2012-09-20 2012-09-21
Third is a table with holiday leave:
Table Holiday
Id_personnel Start_date End_date
3 2012-08-02 2012-08-05
2 2012-02-02 2012-02-15
5 2012-10-01 2012-10-05
I have two event dates: Symposium_start_date and a Symposium_end_date (as variables) and I would like to select all Personnel.Id_personnel and Personnel.Name available for the symposium (not in medical leave or on holiday).
In my example if Symposium_start_date = 2012-10-02 and Symposium_end_date = 2012-10-06 the result must be:
Id_personnel Name
1 John
3 Tom
(as you can see Alice and Charles are on medical leave and Ben on holiday)
Thank you!

Answer 1

For a MS SQL server.
declare #start date = '2012-10-02', #end date = '2012-10-10'
select personnel.*
from personnel
left join holiday on personnel.Id_personnel = holiday.Id_personnel
and holiday.start_date<=#end
and holiday.end_date>=#start
left join medical on personnel.Id_personnel= medical.Id_personnel
and medical.start_date<=#end
and medical.end_date>=#start
where holiday.Id_personnel is null
and medical.Id_personnel is null

Answer 2

assuming MS-SQL, similar to others, but have shown tables unioned together, and subquery that shows all those who conflict with the symposium dates - I think this is easier to write first - and then selecting all those people who are NOT conflicting. Regards!
declare #Symposium_start_date date = '2012-10-02'
declare #Symposium_end_date date = '2012-10-06'
select * from Personnel P where p.Id_personnel not in (
select Id_personnel from (
select m.Id_personnel, m.Start_date, m.End_date
from Medical M
union
select h.Id_personnel, h.Start_date, h.End_date
from Holiday H
) as Leave
where (Start_date between #Symposium_start_date and #Symposium_end_date)
or (End_date between #Symposium_start_date and #Symposium_end_date)
or (Start_date <= #Symposium_start_date and End_date >= #Symposium_end_date)
)

Answer 3

this is an example with the Medical table only. You can easily add the Holiday
declare #Symposium_start_date datetime
declare #Symposium_end_date datetime
set #Symposium_start_date = '2012-08-01'
set #Symposium_end_date = '2012-08-04'
select *
from personel p left join medical m on p.Id_personel = m.Id_personel
where (#Symposium_start_date > m.end_date) or (#Symposium_end_date<m.start_date)