Is an index on varchar column efficient?

[murthy gandikota]

Hi,
   
  I have a table with 2 million records but without an index or a primary key. The column
upon which I want to create an index is a varchar. Will it give me any advantage when I
have to do a select on the column?
   
  BTW, here is the scenario:
   
  create table `test` (`phonenumber` varchar(100));
  insert into test (phonenumber) values(`0001234567');
  and so on 2 million times
   
  alter table test add index (phonenumber)
   
  Also, I can't modify the code that calls the SQL. It was written in VB and the developer
has left the company with the source.
   
  I would like to get your feedback before I actually do this because I don't want to
create a disruption when the DB is in production.
   
  Thanks
  Murthy

       
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