What database are you using?
This could be slightly different from one RDBMS to another.
In oracle you could use the INSTR and SUBSTR functions, and in T-SQL (Sql server) you would use CHARINDEX and SUBSTRING.
For example, the following query would show the separated fields (Oracle):
select substr(field_x,1,instr(field_x,'*')-1) first_field,
substr(field_x, instr(field_x,'*',-1)+1) second_feld
In Oracle it is easier to manage those records that have more than one ‘*’, because you can use a negative ‘start_position’ in the INSTR function, to start searching from the end of the string, which I think is not true with T-SQL.