SQL split the first name with underscore - sql

Question

I'm trying to split the first name from the middle name or middle initial when there's an underscore in the name. I was able to split the first name from the middle name when there is a space, but having trouble with the underscore.
I would like to keep it all together in the case statement if possible.
SELECT
[first name]
, SUBSTRING([first name], 1,
CASE WHEN SUBSTRING(REVERSE([first name]), 2, 1) = ' '
THEN CHARINDEX(' ', [first name]) - 1
ELSE LEN([first name])
END) AS FirstName ,
CASE WHEN SUBSTRING(REVERSE([first name]), 2, 1) = ' '
THEN SUBSTRING([first name], LEN([first name]), 1)
ELSE NULL
END AS MiddleName
, [Last Name]
FROM nametable

Answer 1

The following example uses two case expressions to separate one column into two. It makes use of a feature of Substring: no error is raised if the specified length exceeds the length of the input string.
Note that the sample data is not an image of data, but useful data.
declare #Samples as Table ( Name VarChar(20) );
insert into #Samples ( Name ) values
( 'Billy' ), ( 'Billy Bob' ), ( 'Billy_Joe' ), ( 'Edgar_7' ),
( '_' ), ( 'X_' ), ( '_Y' ), ( '' );
select Name,
case
when CharIndex( '_', Name ) > 0 then Left( Name, CharIndex( '_', Name ) - 1 )
else Name end as FirstName,
case
when CharIndex( '_', Name ) > 0 then Substring( Name, CharIndex( '_', Name ) + 1, 20 )
else NULL end as MiddleName
from #Samples;

Answer 2

Add the REPLACE function inline:
SELECT
[first name]
, SUBSTRING([first name], 1,
CASE WHEN SUBSTRING(REVERSE(REPLACE([first name], '_', ' ')), 2, 1) = ' '
THEN CHARINDEX(' ', REPLACE([first name], '_', ' ')) - 1
ELSE LEN([first name])
END) AS FirstName ,
CASE WHEN SUBSTRING(REVERSE(REPLACE([first name], '_', ' ')), 2, 1) = ' '
THEN SUBSTRING(REPLACE([first name], '_', ' '), LEN([first name]), 1)
ELSE NULL
END AS MiddleName
, [Last Name]
FROM nametable

Answer 3

Thanks to sample data provided by #HABO, you can try this too:
SELECT L.Name,
L.FirstName,
CASE L.MiddleName WHEN '' THEN NULL ELSE L.MiddleName END AS MiddleName
FROM
(
SELECT P.Name,
REPLACE(SUBSTRING(P.UnderscoredName, 1, P.UnderscoreIndex), '_', '') AS FirstName,
REPLACE(SUBSTRING(P.UnderscoredName, P.UnderscoreIndex, LEN(P.UnderscoredName) - P.UnderscoreIndex + 1),'_','') AS MiddleName
FROM
(
SELECT K.Name,
K.UnderscoredName,
CHARINDEX('_', K.UnderscoredName) AS UnderscoreIndex
FROM
(
SELECT Name,
REPLACE(CASE WHEN Name LIKE N'%[_]%' THEN Name ELSE Name + '_' END,' ','_') AS UnderscoredName
FROM #Samples
) AS K
) AS P
) AS L;