Regular expression for email address formats

Question

I have the following regulare expression which I am using to validate email address format.
This allows addresses of the form
[email protected]
^[-a-zA-Z0-9._]+\@[-a-zA-Z0-9]+\.[-a-zA-Z0-9]+\.[-a-zA-Z0-9]+$
And of course this allows addresses of the form
[email protected]
^[-a-zA-Z0-9._]+\@[-a-zA-Z0-9]+\.[-a-zA-Z0-9]+$
What I'm looking for is something which will allow both.

Answer 1

This way
'^[-a-zA-Z0-9._]+\@[-a-zA-Z0-9.]+$' would allow both. :-)
with test_data as
( select '[email protected]' as val from dual union all
  select '[email protected]'   as val from dual union all
  select 'no#good'              as val from dual
select
  val ,
  case
    when regexp_like( val, '^[-a-zA-Z0-9._]+\@[-a-zA-Z0-9.]+$' ) then 'Y'
    else 'N'
    end
    as good
from test_data ;
VAL                  G
[email protected] Y
[email protected]   Y
no#good              NBut then again, it would also allow "[email protected]" and "[email protected]" too. So I suspect you don't really want something that simply allows your two cases to pass validation. If you want to allow only those two cases then try something like this.
with test_data as
( select '[email protected]'     as val from dual union all
  select '[email protected]'       as val from dual union all
  select '[email protected]' as val from dual union all
  select '[email protected]'      as val from dual union all
  select 'no#good'                  as val from dual
select
  val ,
  case
    when
      regexp_like
      ( val
      , '^[-a-zA-Z0-9._]+\@[-a-zA-Z0-9]+\.[-a-zA-Z0-9]+(\.[-a-zA-Z0-9]+)?$'
      ) then 'Y'
    else 'N'
    end
    as good
from test_data ;
VAL                      G
[email protected]     Y
[email protected]       Y
[email protected] N
[email protected]      N
no#good                  N--
Joe Fuda
SQL Snippets
Message was edited by SnippetyJoe - added clarification.