Week Eighteen - CST 363 - Database Systems

Prompt

SQL has the flexibility to join tables on any column(s) using any predicate (=, >, < ).  As long the column(s) are type compatible.   98% of the time the join uses primary key of one table, foreign key of the other table and equal predicate.  Think of example where joining on something other than keys would be needed.  Write the query both as English sentence and SQL.  If you can't think of your own example, search the internet for an example.

Response

One example of such a query could be utilized in online retail to determine which customers made an order within the first day of creating their online account. The customer table would have an account_created_date field and the orders table would have an order_date field. Comparing these non-primary keys would give us this bit of information.

SELECT customer_name

FROM customers c JOIN orders o

              ON c.account_created_date = o.order_date;