To create a join index, use the CREATE JOIN INDEX statement.
For example, suppose that a common task is to look up customer orders by customer number and date. You might create a join index like the following, linking the customer table, the order table, and the order detail table:
CREATE JOIN INDEX cust_ord2 AS SELECT cust.customerid,cust.loc,ord.ordid,item,qty,odate FROM cust, ord, orditm WHERE cust.customerid = ord.customerid AND ord.ordid = orditm.ordid;