Selecting From Multiple Tables—Table Joins

There is no single table with both customer name and order information. So:

   SELECT name FROM customer, sales_order 
   WHERE customer.id = customer_id AND
         order_date = '2004-05-01'; 

• The customer and sales_order tables are "joined".

• Since both tables have an id column, it is qualified by prefixing the table name and dot.

• It's a good idea to always qualify columns:

   SELECT customer.name FROM customer, sales_order 
   WHERE customer.id = sales_order.customer_id AND
         sales_order.order_date = '2004-05-01';