Get Started with Apex Triggers

Get Started with Apex Triggers from (module - Apex Triggers)

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Create an Apex trigger:
Name: AccountAddressTrigger
Object: Account

SOURCE CODE:
trigger AccountAddressTrigger on Account (before insert, before update) {
    for(Account a: Trigger.New){
        if(a.Match_Billing_Address__c == true && a.BillingPostalCode!= null){
            a.ShippingPostalCode=a.BillingPostalCode;
        }
    }
}