Somethnig that I wanted to do the other day was to parse out the different parts of and email address. The user and the domain part. However the data I was using was quite poor. I also wanted to be able to use this information in a computed column.

First of all I tried it this way.

User part

left([EMailAddress],charindex('@',[EMailAddress])-(1))

Domain part

right([EMailAddress],len([EMailAddress])-charindex('@',[EMailAddress]))

Which of course would crash on poor data. So they very quickly turned into functions so they were easyier to change and also decided that they should return null if there was no '@' in the data.

CREATE FUNCTION EMailExtractDomain
      (@EMail VARCHAR(MAX))
RETURNS VARCHAR(MAX)
BEGIN
      DECLARE @idx INT
      DECLARE @domain VARCHAR(MAX)

      SELECT @idx = CHARINDEX('@', @EMail)
      IF @idx = 0
            RETURN NULL

      SELECT @domain = SUBSTRING(@EMail, @idx + 1, LEN(@EMail))
      RETURN @domain
END
GO

CREATE FUNCTION EMailExtractUser
      (@EMail VARCHAR(MAX))
RETURNS VARCHAR(MAX)
BEGIN
      DECLARE @idx INT
      DECLARE @domain VARCHAR(MAX)

      SELECT @idx = CHARINDEX('@', @EMail)
      IF @idx = 0
            RETURN NULL

      SELECT @domain = SUBSTRING(@EMail, 0, @idx)
      RETURN @domain
END
GO

I also ran them though a set of quick tests.

SELECT dbo.EMailExtractUser('nobody@example.com'), dbo.EMailExtractDomain('nobody@example.com')
SELECT dbo.EMailExtractUser('example.com'), dbo.EMailExtractDomain('example.com')
SELECT dbo.EMailExtractUser(''), dbo.EMailExtractDomain('')
SELECT dbo.EMailExtractUser(NULL), dbo.EMailExtractDomain(NULL)

Enjoy