What types of user exits are there in SAP?

What user exit should be used to supress the line item netpr field in production purchase order, if the items have an Info Record? The field is MEPO1211-NETPR.

There are three kind of user exits. You can search for them by looking for: - The string "userexit"
- Customer-function (in case of CMOD/SMOD)
- exithandler (in case of a BAdI, see SE18/SE19)