Serverside events for saving channel entries in the admin area

Hi there, Iam new to expression engine and would like to know is it possible to write custom code for the channel entries screen in the admin area?

Specifically what i like to do is: 1. When a new channel record is saved, i would like to do a uniqueness check on a particular field. If there is already an existing value, alert the user that the new channel entry cannot be added 2. Similarly when a new channel record is saved, i would like to run a custom sql query to inject a record into another table eg say iam saving a channel record - a user id and a product id, i would like to update the total spend field for that user on the user table.

Appreciate if anyone can guide me the most appropriate way to do the above..

thanks

al

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