Introduction In this article, we are going to see how a CROSS JOIN works, and we will also make use of this SQL join type to build a poker card game. Database table model For our poker card game application, we have created the ranks and suits database tables: The ranks table defines the ranking of cards, as well as the name and symbol used for each card rank: The suits table describes the four possible categories used by the French playing cards: Cartesian product In the set theory, the Cartesian product... Read More
By “Good SQL Querying”, I am not referring to “how to make your queries more perfomant.” I am about to go on a mini-rant about how to make readable and self-documenting SQL queries.
One practice that will get me instantly going on a rant is using a comma join. There is NO reason to do the following:
-- uses the sakila sample database SELECT first_name, last_name, address FROM customer,address;
What kind of join did the original author intend? A CROSS JOIN? Or did they really want an INNER JOIN and forget the WHERE clause?
The answer: you do not know for sure; you can only guess. Had the query been
SELECT first_name,last_name,address FROM customer INNER JOIN address;
you would know that the author intended an INNER JOIN; had the query been
SELECT first_name,last_name,address FROM customer CROSS JOIN address;
you would know that the author intended a CROSS JOIN. I …[Read more]