public static void setAccount(List<Account> newList){
    List<Account> pirList = new List<Account>();    
    List<Account> p1 = new List<Account>();
    for(Account newAcc: newList){
            
            if(newAcc.RecordTypeId == pirRecId){
                p1.add(newAcc);
                
                p1 = [SELECT id,FirstName,LastName,MiddleName 
                                FROM Account 
                                WHERE
                                FirstName =: newAcc.FirstName AND
                                LastName =: newAcc.LastName AND
                                MiddleName =: newAcc.MiddleName ];

                for(Account patient:p1){
                    patient.lookup = newAcc.Id;
                }
                update p1;
            }
        }    
   }
This function is called from a trigger in after insert

public static void setAccount(List<Account> newList){
    List<Account> pirList = new List<Account>();    
    List<Account> p1 = new List<Account>();
    for(Account newAcc: newList){
            
            if(newAcc.RecordTypeId == pirRecId){
                p1.add(newAcc);
                
                p1 = [SELECT id,FirstName,LastName,MiddleName 
                                FROM Account 
                                WHERE
                                FirstName =: newAcc.FirstName AND
                                LastName =: newAcc.LastName AND
                                MiddleName =: newAcc.MiddleName ];

                for(Account patient:p1){
                    patient.lookup = newAcc.Id;
                }
                update p1;
            }
        }    
   }
This function is called from a trigger in after insert

If I am using below Query
SELECT CaseNumber from Case where  ClosedDate > LAST_N_DAYS:31

To get all case numbers  which have been closed within last 30 days , It is not giving any result , even though Some cases exist in Database closed within the 30 days.

I could not understand , why I am not getting correct result.
Thanks
Yogendra Rishishwar