What is an “upsert” DML statement in Salesforce?
DML stands for Data Manipulation Language.
UPSERT is a one of the DML operation.
When a record is upserted (ex: upsert account/contact record;), the system updates the account/contact record if it already exists. Else, the account/contact record is inserted.This operation is particularly very helpful when you have a set of records of which a few have to be inserted and others updated. The upsert operation combines both insert and update into one.