A value of 0 is returned if the string is not found.
CHARINDEX does not take into account whether the strings are upper or lower case.
8> DECLARE @STRING_TO_SEARCH_FOR varchar(4)
9> DECLARE @STRING_TO_SEARCH_WITHIN varchar(100)
10> SET @STRING_TO_SEARCH_FOR = "rntsoft.com"
11> SET @STRING_TO_SEARCH_WITHIN = "rntsoft,rntsoft.com, www.rntsoft.com"
12> SELECT CHARINDEX(@STRING_TO_SEARCH_FOR, @STRING_TO_SEARCH_WITHIN, 6)
13> GO
-----------
8
(1 rows affected)