difference between first fast and first only IN SQL command

when we  run this  SQL command in  job

select firstonly  from custtable where CustTable.Name=="Rohit";

here the SQL statement will fetch only first record and then it will stop


when we run  select firstfast from custtable where CustTable.Name=="Rohit";

it will  fetch the first record fast and then later it will fetch all the records slowly  after the first record is fecthed. (matching with the  condition/s applied)


please note time taken to fetch the first record in both the scenario are the same.........  only diffrence is that  firstonly   will get only 1 records where as other one will fetch others records which matches the certain critirea