Trigger Scenarios

 1) Duplicate contact on same object phone and email

   Trigger DuplicateRecordemailandphone on contact(before insert){

   set<string> setemail = new set<string>();

   set<string> setphone = new set<string>();

    for(contact con:trigger.new){

    setemail.add(con.email);

    setphone.add(con.phone);

       }

   list<contact> conts = [select id,lastname,email,phone from contact where email in: setemail AND  

                                       phone in: setphone ];

        for(contact contem:conts){

      if(conts.size() > 0){

         contem.email.addError('Duplicate email Not Allowed');

           }

         } 

   }

  2) Trigger is designed to recalculate and update a custom field 'TotalAmount__c' on the related                    Account Records wherever opportunities are insert updated or deleted

    Trigger UpdateValueAmount on Opportunity (after insert, after update, after delete){

     set<id> accountIds = new set<id>();

    if(Trigger.isInsert && Trigger.Isupdate){

      for(opportunity opp:trigger.new){

      accountIds.add(opp.AccountId);

          }

      }

         if(Trigger.isDelete){

        for(opportunity opp:trigger.old){

        accountIds.add(opp.AccountId);

             } 

        }

       list<Account> updateAccounts = new list<Account>();

    for(Account acc : [select id,Name, (select id,Amount from opportunities)from account where Id in :              accountIds]){

       Decimal totalAmount = 0;

     for(opportunity opp : acc.Opportunities){

     totalAmount += opp.Amount;

       }

      acc.TotalAmount__c = totalAmount;

       updateAccounts.add(acc);

        }

  update updateAccounts;

       }

3. Use Case:-  Account Object  Has Field numberofcontact__c when you create the account enter the value   of 10 automatically create 10 contact record

Trigger UpdateValuesCount on Account(after insert){

list<contact> conlist = new list<contact>();

for(Account acc:Trigger.new){

 integer int = acc.numberofcontact__c;

 if(int.numberofcontact__c = null && int.numberofcontact__c > 0){

 for(integer i=0;i<int;i++){

  contact con = new contact();

  con.lastname = 'Giri Kumar' + String.Valueof(i + 1);

  con.firstnmae = 'Bingi';

  conlist.add(con);

 }

}

}

 insert conlist

}