Algo como esto:
Código SQL:
Ver originalDECLARE @variable VARCHAR(MAX)
SET @variable='Site Index=252, Cell Index=252, Alarm Cause=Other causes, Site Type=BTS3900E, Site Name=S_YOMBLON, Cell Name=AM02520, Cell CGI=716-06-1041-4f1a'
SELECT SUBSTRING(SUBSTRING(@variable,charindex('S_',@variable,1),len(@variable)),1,(charindex(',',SUBSTRING(@variable,charindex('S_',@variable,1),len(@variable)),1))-1)
Saludos!