Check Duplicate Records

Question

Hi All,

I have a my sql database with 300000 records, Every month I need to insert 50000 records to database.

The way I have done this is,

I have put select comand and it is check thoes 50000 records one by one with 300000 records and if the duplicate not found it is insert to database.

above way it is takin 12 hours to complete the task, This is not under requirement.

I need avoid this much time take for this matter, and If i can do this with in 2 or 3 hours It will be grate.

Please help me someone