Upsert Statement..

The upsert DML operation creates new sObject records and updates existing sObject records within a single statement, using an optional custom field to determine the presence of existing objects.

This example performs an upsert of a list of accounts.

List<Account> acctList = new List<Account>();
// Fill the accounts list with some accounts

try {
    upsert acctList;
} catch (DmlException e) {
   
}

This next example performs an upsert of a list of accounts using a foreign key for matching existing records, if any.

List<Account> acctList = new List<Account>();
// Fill the accounts list with some accounts

try {
    // Upsert using an external ID field
    upsert acctList myExtIDField__c;
} catch (DmlException e) {
   
}