Chart iReport compare same fields in different dates.

Hi, i have some charts and need to create one that is able to compare the same fields in different dates( months and years).

My  date_field is a string. For a chart that gives me all the expenses between two dates i use :

where  STR_TO_DATE(date_field,'%d-%m-%Y') BETWEEN $P{DATE_ONE} AND  $P{DATE_TWO}.

Now i need to show it in two or more categories, each one  will show values that belongs to a year.

Does someone have an idea or example, tutorials?