improving indexes

[Patrice De Cafmeyer]

hi,

I have pretty bad performance on the following query. Could someone help me to define 
the indexes I need on the tables to improve this.
Thanks in advance.

select a.field_1,a.date,b.field_1,b.field_2,sum(a.subtotal) as total
 from table_a as a, table_b as b
 group by b.field_2,a.field_1 
 having month(a.date)=10 and a.field_1=b.field_1
 order by b.field_2 asc, a.date desc


Roswell