Popup Should come before insert

[waqas]

hi all,

i have a form for inserting leave in my database columns as

id, startdate, enddate and leavetype. i insert below leave

4120 , 01-Sep-11 , 15-Sep-11 , Annual leave.

if i insert 4120, 05-Sep-11, 10-Sep-11, Sick leave



it should tell me that leave already exist in these dates.

how can any one help me?

[RuralGuy]

This link may be of help: http://allenbrowne.com/appevent.html