Splitting a Full Name Apart When It Has Been Stuffed into a Single Field

-- In case the need arises to split a comma-delimited name - for example, where the last and first name have been stuffed into the same field such as 'Lastname, Firstname'

SELECT [UserName]
  , RTRIM(LTRIM(LEFT([FieldName], CHARINDEX(',', [FieldName]) -1))) [LastName]
         , RTRIM(LTRIM(STUFF([FieldName], 1, CHARINDEX(',', [FieldName]), ''))) [FirstName]
FROM [DatabaseName].[dbo].[TableName]