About caching the data

Question

HI

first i need to check whether key is present in database table or not,

If it is not thr means i need to insert one key in table and after that i need to retrive data.

I need to compare datime which is present in table and present time ,if it is lessthan means i need to retrive from table else i need to reinsert data to table and retrive from it

Plz send sample code

 

Thanks.