Use sp_drv_univarchar_charindex which accesses the Transact-SQL function charindex.
sp_drv_univarchar_charindex search_string, locator, start, position
search_string – the literal, of type univarchar, to search for.
locator – a unitext_locator that references the unitext column to search from.
start – an integer specifying the position from which to begin searching. The first position is 1.
position – an integer specifying the starting position of search_string in the LOB column referenced by locator.
None.
