In a data warehouse, you often need to join several large tables. Let’s assume you have ORDERS and ORDER_ITEMS tables defined as follows:
CREATE TABLE orders ( id INT, created DATE, customer VARCHAR(100) ); CREATE TABLE order_items ( id INT, order_id INT, product_id INT, qty INT, price DECIMAL(9,2) );
You can use the following query to get all order items:
SELECT * FROM order o, order_items i WHERE o.id = i.order_id
Both tables can be very large, containing hundreds of millions rows each.
Join in Traditional MPP Systems
First, let’s see how this problem is solved in traditional MPP systems such as Teradata, DB2 DPF, Greenplum and others.