Excuse the formatting, it seems the interface likes it like this!!!! But as an alternative, something like this:-

CREATE TABLE #testme(ConvertMe varchar(20));

INSERT INTO #testme (ConvertMe )

VALUES ('123') ,('665584'),('13.4'),('16.8.7'),('1.2.1'), ('1'), ('1.1'), ('1.1.1'),('10.8.7.5.2')

SELECT

CASE

WHEN CHARINDEX('.', ConvertMe) < 2 THEN CONVERT(DECIMAL(10,1), ConvertMe)

ELSE CONVERT(DECIMAL(10,1),LEFT(ConvertMe, CHARINDEX('.', ConvertMe) + 1))

END NewVal

FROM #TestMe

DROP TABLE #testme